Resources » Terminology

Natare Terminology

a b c d e f g h i j k l m n o p q r s t u v w x y z



    see free available chlorine

  • ACID

    a sour chemical substance containing hydrogen with the ability to dissolve metals, neutralize alkaline materials and combine with bases to form salts; acid is used to lower (decrease) pH and total alkalinity of swimming pool and spa water; examples are muriatic acid (hydrochloric) and dry acid (sodium bisulfate)

  • Acid DEMAND

    amount of acid needed to lower pH to the proper level for pool water


    reagent test usually used in conjunction with a pH test to determine the amount of acid needed to lower pH and total alkalinity levels


    precipitation having an unusually low pH value (4.5 or lower) caused by absorption of air polluted by sulfur dioxide, carbon dioxide and nitrous oxide


    1. to kill algae; algaecides perform best as a backup to a routine sanitation program
    2. help to kill airborne spores as they blow into the pool

    retards and prevents algae genesis and growth

  • Algae

    1. microscopic plants deposited in pool or spa water by wind, rain and dust, they thrive in sunlight and warm water, clogging pool equipment and causing slippery surfaces and green water; there are 21,000 known species of algae
    2. algae are not disease causing, but can harbor bacteria, and it is slippery
    3. most common pool types are black, blue-green, green and mustard (yellow or drawn)
    4. pink or red-colored algae-like organisms exist but are bacteria and not algae; maintaining proper sanitizer levels, shocking and superchlorination will help prevent algae occurrence

    1. basic chemical that neutralizes acids by releasing carbonates and/or hydroxides
    2. also called base
    3. the opposite of acid
  • Alkaline

    when pool water measures above 7.0 on the pH scale

  • Alkalinity

    1. amount of carbonate, bicarbonate and hydroxide compounds in pool water
    2. more commonly called total alkalinity
    3. measure of the pH-buffering capacity of water
    4. also called the water’s resistance to change in pH
    5. one of the basic water tests necessary to determine water balance
  • Alum

  • Ammonia (NH3)

    1. nitrogen-containing compound that combines with free chlorine to form chloramines; chloramines have a strong chlorine odor and can cause skin and eye irritation
    2. introduced into the water by swimmers as waste (perspiration or urine) or by other means; quickly forms foul-smelling, body-irritating chloramine – a disabled, less- effective form of chlorine

    chemical added to the water to make the sud or foam disappears; these products do not remove the source of the sudsing; most often, the water must be drained and refilled to remove the soaps, oils and other causes of foaming; shocking and superchlorination may help prevent foaming

  • ampere/hour (AH)

  • authorized release device

    device that allows authorized persons to enter or exit monitored and controlled openings without triggering an alarm; the authorized passage release may be a keyed switch, a card reader, a digital code reader

  • automatic surge

    device incorporated into a stainless steel perimeter

  • arc

    electrical current through air or across the surface of an insulator associated with high voltage; usually occurs when a contact is opened, de-energizing an inductive load; arcing of a contact will limit its life

  • annunciator

    audible and/or visual signaling device

  • ampere (amp)

    unit of measurement for the rate of electrical current flow; one ampere is the current flowing thorough one ohm of resistance at one volt potential

  • American Wire Gauge (AWG)

    standard system in the United States for designating wire size (diameter of metal)

  • American Society for Testing Materials (ASTM)

    organization that tests materials and attempts to set standards on various materials for industry

  • alternating current (AC)

    electric current that reverses its direction regularly and continually; the voltage alternates its polarity and direction of current flow negative to positive

  • airtraps

    see interlock

  • adjustable

    ability to change or alter time delay or other parameter by means of adjustment, such as a potentiometer, resistor, or switch

  • access control

    means of influencing and regulating flow of persons through a door, entry and/or exit alarm

  • Automatic Surge

    device incorporated into a stainless steel perimeter


    thermoplastic sheet formed into a mold to make a spa or related equipment; it is first heated and then vacuumed onto the mold


    located on the top of the filter, sometimes accompanied by a pressure gauge, the bleeder is opened to release air trapped in the filter


    mechanical device that forces air through holes in the floor, bubbler ring or hydrotherapy jets in a spa


    1. brass or plastic, manually operated valve located at the top of a filter tank for relieving the pressure inside the filter and for removing the air inside the filter (called bleeding the filter)
    2. sometimes called a pressure-relief valve

    device, which agitates or vacuum debris from the walls and floor of the pool automatically

  • AWS Systems

  • Access Equipment

    variety of equipment designed to facilitate entrance and egress from a pool; may include ladders, lifts, steps or boards

  • Above-ground (On-ground) pools

    pools that are portable and removable; a frame that is located entirely above ground and can be disassembled

  • Age group swimming

    1. a structure of the U.S. Swimming organization where children break up into groups according the their age and ability and work on swimming technique and endurance with the help of a trained coach
    2. nationally recognized age groups are 10 and under, 11-12, 13-14, 15- 16, 17-18 and 15-18; local swim meets may include events for 8 and under
  • Anchor

    last swimmer in a relay

Back to Top



    1. arrangement of pipes, gates and valves by which the flow of water may be passed around a piece of equipment or diverted to another piece of equipment
    2. a controlled diversion

    kills bacteria; chlorine is a bactericide and germicide; silver "algaecides" are actually more bactericide, and are useful on pink "algae"


    1. sodium bicarbonate
    2. white powder used to raise the total alkalinity of pool or spa water without having much affect on pH
  • Balanced Water

  • BASE

    see alkali


    see acid demand

  • Biguanide



    1. condition caused by too much copper not chlorine in the pool water; the copper may get into the water by the bad practice of placing trichlor tabs in the skimmer; this acidic product will cause low-pH water, which will in turn dissolve metals in the equipment; the dissolved metal (usually copper) then stains hair, fingernails and, eventually, pool walls
    2. can also be caused by keeping the pH too low or misusing acid
  • Breakpoint Chlorination

    process of adding sufficient free available chlorine to completely oxidize all organic matter and ammonia or nitrogen compounds; all chlorine added after that point is free available chlorine


    1. by-products formed when bromine reacts with swimmer waste, nitrogen or fertilizer
    2. active disinfectants that do not smell although high levels are body irritants
    3. removed by superchlorination or shock treating
    4. a combined bromine-ammonia molecule; unlike chloramines, which are strong smelling and offer no sanitizing properties, bromamine compounds continue to sanitize

    1. a common term for a bromide salt used to supply bromide ions to the water so they may be oxidized or changed into hypobromous acid, the killing form of bromine
    2. used as a disinfectant

    mechanical or electrical device for dispensing bromine at a controlled rate; most often a canister or floater filled with tablets of bromine

  • Bromine (BR2)

    1. chemical used in various compound forms to sanitize pool and spa water
    2. it forms hypobromus acid in water
    3. available as a tablet or as sodium bromide, a granular salt
    4. member of the halogen family
    5. used as a sanitizer in spas, because of its resistance to hot water with rapid pH fluctuations

    1. substance or compound that stabilizes the pH value of a solution
    2. water’s resistance to change in pH


    single-celled microorganisms of various forms, some of which are undesirable or potentially disease-causing; bacteria are controlled by chlorine, bromine or other sanitizing and disinfecting agents

  • brownout

    low line voltage that can cause misoperation of and possible damage to equipment

  • breakdown voltage

    voltage at which insulation between two conductors is destroyed

  • break

    open an electrical circuit


    correct ratio of mineral content and pH level that prevents the water from being corrosive or scale forming

  • battery standby

    means of automatically switching over to stored battery power during local primary power failure

  • Bather Load

    number of people in a pool or spa at a particular time or during a specific period of time


    electrical device that produces a continuous rush of air to create the optimal bubbling effect in a spa, hot tub or whirlpool; it is usually plumbed with the hydrotherapy jets or to a separate bubbler ring


    repositioning of the soil after construction of a pool


    backing up of water through a pipe in the direction opposite to normal flow

  • Backstroke Flags

    colorful vinyl pennants spaced and sized to meet competitive swimming requirements; generally placed five yards (short coarse) or five meters (long course) from the end of the pool; they enable backstrokers to execute a backstroke turn more efficiently by counting their strokes

  • Backwash

    reversing flow of water through the filter to clean the elements and filter medium

  • Backwash Cycle

    time needed to backwash (clean) the filter and its components using a reverse flow of water


    device with a hollowed out ball inside which can be turned with an external handle to decrease or increase flow


    secondary to the filter pump, a booster pump is used to power an automatic pool cleaner such as Polaris or Letro

  • BTU

    1. abbreviation for British Thermal Unit; the amount of heat necessary to raise 1 lb. of water 1 degree Fahrenheit
    2. a unit of measurement for the use of gas by a gas appliance; pool heaters are rated by their consumption
  • Backstroke flags

    see flags

  • Bulkhead

    a wall constructed to divide a pool into different courses such as a 50-meter pool into two 25-yard courses

  • Block

    starting platform

Back to Top



    1. a granular chemical added to the pool water, which provides a shield to chlorine for protection from UV radiation, which disrupts the molecule, destroying its sanitizing ability
    2. also called stabilizer conditioner

    see clarifier


    see chlorine combined


    any microparticle or organism, which reduces water clarity or quality, or presents health hazards


    effective algaestat and algaecide, copper as elemental is used in many pool products


    chemical compound that contains the element copper; too much copper in the water can cause green-colored stains; newer copper algaecides contain an ingredient that prevents the copper from staining but does not affect copper’s ability to kill algae; these special copper algaecides are called chelated copper algaecides


    similar to aluminum sulfate, this chemical provides a coagulating and flocculent function in water; used in ponds; this amount of copper would stain swimming pools

  • Conditioned Water


    see cyanuric acid

  • Corrosion


    chemical compound that when used in conjunction with chlorine makes the chlorine perform better as an algaecide


    primary in the make up of total alkalinity and total dissolved solids


    1. naturally occurring polymer found in the shells of crabs and lobsters
    2. contained in the some proprietary pool products, chitin acts as a coagulant and flocculent for oils, metals and organic materials

    (pronounced KEY-late)

    1. process of preventing metals in the water from combining with other components in water to form colored precipitates that stain the pool walls and bottom or produce colored water
    2. also called a sequestering agent

    algaecides that contain a special ingredient to prevent the copper from staining the pool walls and bottom or producing colored water


    similar to sequestering agents, a chelating agent is a water soluble molecule that can bond tightly with metal ions, keeping them from coming out of suspension and depositing their stains and scale onto pool surfaces and equipment

  • Chemical Feeder

  • Chloramines


    see isocyanurate


    mechanical or electrical device for dispensing chlorine at a controlled rate; most often a canister or floater filled with tablets of chlorine

  • Chlorine (Cl2)

    1. most widely used bacteria-killing agent for pool water; organic chlorine is more suitable than inorganic for pool use because it is generally easier to use, does not affect water balance as much and is non-clouding
    2. oxidizes ammonia and nitrogen compounds (swimmer and bather waste)
    3. member of the halogen family of sanitizers, its use in swimming pools is in the elemental form of a gas, or as a liquid, granular or tablet compound

    see free available chlorine

  • CHLORINE combined

    1. portion of total available chlorine left over when free available is subtracted
    2. measure of chlorine that has already combined with other molecules or organisms, primarily chloramines
  • CHLORINE total available

    sum of combined and free chlorine levels; with a DPD test kit, one determines free available level, then total available; the difference, if any, is the level of combined chlorine


    quantity of free available chlorine removed during the process of sanitizing; the amount of organic and non-organic material contained in the water will "demand" a certain level of oxidizer to be destroyed


    electrical device that generates chlorine from a salt solution in a tank or from salt added to the pool water


    term that implies that an over abundance of cyanuric acid (stabilizer or conditioner) in the water would cause the chlorine to be all "locked up;" this is not true

  • chlorine NEUTRALIZER

    1. chemical used to make chlorine harmless; used in test kits to counteract the bleaching effect of the chlorine or bromine in order to increase the accuracy of pool water tests
    2. sold as chlorine and bromine neutralizer, it is used to destroy excessive amounts of chlorine or bromine, so the high levels will not affect swimmers

    see residual chlorine


    1. also called coagulant or flocculant
    2. chemical compound used to gather (coagulate or agglomerate), or to precipitate suspended particles so they may be removed by vacuuming or filtration; there are two types
  • Calcium Chloride (CaCl2)

    1. soluble salt added to pool water to raise the calcium hardness level
    2. commonly used for snow melting
  • Calcium Hypochlorite CA(OCL2)

    see hypochlorite

  • Calcium Hardness


    crystalline compounds formed in swimming pool and spa water when the calcium, pH and total alkalinity levels are too high; once formed, the crystals adhere to the plumbing, equipment, pool walls and bottom; these crystals are better known as scale

  • current

    flow of electrons through a conductor; current is measured in amperes

  • continuous duty locking unit

    electric lock equipped with a heavy-duty solenoid that can be energized indefinitely

  • continuous duty

    device or control that can operate continuously with no off or rest periods

  • continuity check

    test performed on a length of wire or cable to determine whether the electrical current flows continuously throughout the length

  • continuity

    state of being complete and uninterrupted, like a normally closed circuit

  • contacts

    electrically conductive points, or sets of points, used to make or break an electrical circuit mechanically

  • connector

    any device used to provide rapid connect/disconnect service for electrical cable and wire terminations

  • conduit

    tube or trough for protecting electrical wires or cables

  • conductor

    material with the ability to carry electric current; the term is also used for an electric wire

  • coil, electric

    successive turns of insulated wire that create a magnetic field when an electric current is passed through them


    switch, which allows manual override of an electrical circuit. It also automatically breaks the circuit when current fluctuations are detected


    mechanical device in a pipe that permits the flow of water or air in one direction only

  • circuit

    path through which electrical energy flows

  • circuit, closed

    1. electrical circuit in which current normally flows until interrupted by the opening of a switch or a switch-type electronic component
    2. circuit or switch in which the contacts are closed during normal operation
  • circuit, open

    1. electrical circuit in which current does not flow until permitted by the closing of a switch or a switch-type electronic component
    2. circuit or switch in which the contacts are open during normal operation
  • closure

    point at which two contacts meet to complete a circuit

  • code

    see national electrical code

  • Cover, Thermal

    cover that retains heat and prevents water evaporation


    cover that is secured around the perimeter of a pool, spa or hot tub that provides a barrier to bathers and debris when the pool, spa or hot tub is closed for the season


    cover that, when placed on the water’s surface of a pool, spa or hot tub, increases the water temperature by absorption and transmission of solar radiation; reduces evaporation and prevents wine-borne debris from entering the water


    cover used on pools, spas and hot tubs that rests on the lip (coping) of the pool or spa deck – not a flotation cover; used as a barrier to swimmers and bathers, and for maintenance and thermal protection


    plumbing fitting designed to join two pieces of pipe


    cap or top lip on the pool or spa wall that provides a finished edge around the pool or spa; it can be formed, cast in place or precast, or prefabricated of extruded aluminum or rigid vinyl; it may also be part of the system that secures a vinyl liner to the top of the pool wall


    degree of transparency of waterCONDUIT


    "circuit" of plumbing which continuously carries the water out of the pool, through the pump & filter, and returns it to the pool


    pump consisting of an impeller fixed on a rotating shaft and enclosed in a casing or volute and having an inlet and a discharge connection; the rotating impeller creates pressure in the water by the velocity derived from the centrifugal force


    pool or spa water filter that uses a replaceable porous element made of paper or polyester

  • Code of Conduct

    agreement signed by a swimmer prior to travel stating that the swimmer will abide by certain behavioral guidelines

  • Coping

    deck tile, usually about one foot wide, at the edge of the pool

  • Course

    designated distance over which the competition is conducted; standard is 25 meters for summer league meets, 50 meters for Olympic competition, and 25 yards for regular year-round and college competition

  • Cut

    1. slang for qualifying time
    2. time standard necessary to attend a particular meet or event
  • Circle Swimming

    performed by staying to the right of the black line when swimming in a lane, to enable more swimmers to swim in each lane

Back to Top


  • Dry Acid

    1. sodium bisulfate
    2. lowers pH and total alkalinity to proper levels

    see anti-foam


    1. common name for sodium dichlor
    2. fast dissolving chlorine compound containing chlorine and cyanuric acid (stabilizer or conditioner); it has a neutral pH and is quick-dissolving, so it can be used for regular chlorination or superchlorination

    see overdrain


    to kill all pathogenic (disease-causing) organisms


    chemicals or processes, which work to destroy vegetative forms of microorganisms and other contaminants; examples are chlorine, bromine, Soft-Swim, ionizers and copper and silver algaecides


    demand that your pool has for dirt; this level is invertedly proportional to available time for cleaning; if you remove the dirt from the pool, you have created a dirt deficit, and the pool will actually suck dirt out of the air to maintain its dirt demand


    see overdrain

  • DPD (Diethyl-P-Phenylene Diamine)

    a test reagent used to measure the amount of available chlorine in pool water; measures both total and free chlorine

  • de-energize

    to remove power

  • dynamic head

  • dry contact

    metallic points making (shorting) or breaking (opening) a circuit; the switched circuit must have its own source of power and is merely routed through the dry contacts

  • double pole, double throw (DPDT)

    1. switch or relay output contact form (2 form C) in which two separate switches are operating simultaneously, each with a normally open and normally closed contact and a common connection
    2. used to make and break two separate circuits
  • door status switch (DSS)

    used to monitor whether a door is in an opened or closed position

  • direct current (DC)

    electrical current that travels in only one direction and has negative (-) and positive (+) polarity; it may or may not have an AC ripple component; DC sources that are unfiltered should be referred to as full-save or half-wave rectified AC

  • delay on make

    see delay on energization

  • delay on energization

    1. mode of operation relative to timing devices; delay begins when initiate switch is closed or on application of power to input
    2. also called delay on make
  • delay on break

    mode of operation relative to timing devices; delay begins when the initiate switch is opened (delay on break of initiate switch)

  • decibel (dB)

    increment of measurement used to compare measured levels of sound energy (intensity) to the apparent level detected by the human ear; expressed as a logarithmic ratio (sound that has 10 times the energy of another sound is said to be 10 decibels louder; 100 times the energy is 20 decibels louder; 1,000 times the energy is 30 decibels louder; and so on); decibel levels are correctly expressed as the number of decibels at a measured distance from source of sound (for example,125 dB at 10 feet)


    areas immediately adjacent to a pool or spa that are specifically constructed or installed for use by bathers for sitting, standing or walking

  • D. E. FILTER (Diatomaceous Earth Filter)

    filter designed to use diatomaceous earth (D.E.) as the filter medium; the D.E. is added through the skimmer with the pump on, which takes the D.E. and deposits it on a grid; the D.E. then becomes the filter medium



    1. also called D.E.
    2. white poder composed of fossilized skeletons of one-celled organisms called diatoms; the skeletons are porous and have microscopic spaces; the powder is added through the skimmer with the pump on and deposits itself on a grid; the powder then becomes the filter medium
  • Diatomaceous Earth Filter

    see D.E. Filter


    1. porous plate, tube or other device through which air is forced and divided into minute bubbles for diffusion in the water
    2. an over drain on a sand filter
    3. used on a closed-face impeller on a pump to concentrate water flow to the center of the impeller

    1. also called TDS or total dissolved solids
    2. a measure of the total amount of dissolved matter in water; examples are calcium, magnesium, carbonates, bicarbonates, sodium, chlorides and metals; high levels can cause corrosion, colored water or salty taste; maximum level is usually 2500 ppm for pools; maximum level for spas is 1500 ppm over starting level
  • Diving Board

    see springboard

  • Drain (vacuum to waste)

    this useful setting allows you to vacuum large volumes of debris that would either clog the filter or pass through it because of its small size; dirt that is vacuumed passes right out the waste line; it is also the setting of choice when draining the pool or lowering the water level


    1. plumbing fitting installed on the suction side of the pump in pools, spas and hot tubs
    2. sometimes called the main drain, it is located in the deepest part of the pool, spa or hot tub, it is not a drain, such as a drain on a kitchen sink; main drains do not allow the water to drain to waste but rather connect to the pump for circulation and filtration
  • Distance

    events over 400 meters/500 yards

  • Dual Meet

    competition between two clubs

  • Dryland Training

    training done out of the water that aids; enhances swimming performance

  • Drill

    an exercise involving a portion or part of a stroke, used to improve technique

  • DQ

    disqualification from an event

  • Divisionals

    championship meet of the summer league season


    recreational mechanism for entering a swimming pool, consisting of a semi-rigid board that derives its spring from a fulcrum mounted below the board and attached to the deck

Back to Top



    1. electrochemical reaction causing a black stain normally found around metal fixtures or on the plaster; caused by two dissimilar metals being plumbed together or from an improper electrical grounding of pool equipment or lights
    2. decomposition of water and other inorganic compounds in aqueous solution by means of electricity; chlorine generators use this principle to produce chlorine from salt in the water

    designed to break down and digest oils


    1. power to produce an effect
    2. chlorine’s efficacy is affected by many factors, including the sun, water balance and the water’s chlorine demand
  • energize

    to apply power

  • equalizer line

    line from below the pool surface to the body of a skimmer, designed to prevent air being drawn into the filter when the water level drops below the skimmer inlet; operates automatically


    water that flows out of the pump, on its way through the filter, heating and treating equipment, and returning to the pool; also known as the pressure side


    plumbing fitting shaped at a 90-degree or a 45-degree angle usually made of metal, PVC or plastic


    ornamental shield, flange or border used around a pipe, plumbing fitting, grab rail or light

Back to Top


  • FREE Available CHLORINE

    1. free chlorine in the pool or spa water that is available to sanitize or disinfect the water
    2. hypochlorous acid, the chlorine in pool water that is not combined with ammonia or nitrogen and therefore available to kill bacteria entering the pool
  • FOAM

    froth of bubbles on the surface of the water; usually from soap, oil, deodorant, hair spray, suntan oil, etc., that is shed into the water as swimmers enter

  • Flocculating Agent

    see clarifier


    combination, agglomeration, aggregation or coagulation of suspended particles in such a way that they form small clumps or tufts (called floc)


    see clarifier

  • FLOC

    clump or tuft formed when suspended particles combine with a flocculating agent


    surface foam on water caused by high TDS levels

  • FILM-X

    1. compound of citric acid used in cleaning plaster and other pool areas
    2. safe replacement for muriatic acid

    used in filling or adding to the water level

  • fuse

    protective device, placed in a circuit as a safeguard, that contains a strip of easily melted metal; when the current flow becomes too great, the metal melts, thus breaking the circuit

  • face piping

    piping, with all valves and fittings, used to connect the filter system together as a unit

  • fail safe

    see fail-unlocked

  • fail secure

    see fail-locked

  • feet of head

    basic measurement of pressure or resistance in a hydraulic system, which is equivalent to the height of a column of water that would cause the same resistance

  • fire door latch

    latch that has a 1/4-inch throw and an anti-friction reactor

  • form c contact

    switch mechanism that contains three terminals (normally open, common, and normally closed)


    mechanical switch located inside the time clock, which opens a circuit and shuts off the heater 10 or 15 minutes prior to shutting off the water circulation pump, allowing the heater to cool down; this helps reduce lime buildup in the heat exchanger

  • Foot Bath

  • Flow Rate

    volume of liquid flowing past a given point in a specific time period, expressed in gallons per minute or hour

  • Flow Meter

    measuring device that determines the gallons per minute of water flow through a pool re-circulation system


    rate of water pumped through a filter, in gallons per minute (gpm)


    fine spun filaments of glass which are available in a rope or mat form; when used in a process with polyester resins, catalysts and hardeners can be formed or molded into pools, spas and related shapes

  • Filter

    mechanical device for straining suspended waste particles from the pool as water circulates through a porous substance called a filter medium; refers to the complete mechanism including all components; the three types of filters used in pools and spas are sand, cartridge and D.E. (diatomaceous earth)


    chemical compound added to the water or to the filter that allows the existing filter to become more efficient; examples are alum, water clarifiers and D.E. (diatomaceous earth)


    total surface area of the filter medium that is exposed to the flow of water from the pump, expressed in square feet


    replaceable porous element made of paper or polyester used as the filter medium in cartridge filters


    1. operating time between cleaning or backwashing cycles of a filter
    2. amount of time the filter has water flowing through it each day expressed in hours
  • Filter Element

    porous component in the filter tank that removes particles and other suspended wastes from water before its re-circulated back to the pool

  • filter latErals

    see underdrain


    finely graded material, such as sand, diatomaceous earth, polyester fabric or anthracite coal that removes suspended particles from water passing through it


    common name for diatomaceous earth (D.E.), used as the filter medium in a diatomaceous earth filter


    device that pulls water from the pool and pushes it through the filter on its way back to the pool


    graded, rounded rock and/or gravel used to support the filter medium; usually used with rapid-rate sand filters

  • Filter Sand

    sharp silica or quartz particles graded for uniform size and used as a filter medium


    portion of the filter element consisting of cloth, wire screen or other porous material on which the filter medium or filter aid is deposited; nylon grid on a D.E. filter is the septum

  • Face Piping

    piping, with all valves and fittings, which is used to connect the filter system together as a unit; this includes all valves and piping necessary for the filter plant to perform the functions of filtering or backwashing, either by the plant as a whole or any unit operating singly

  • Flags

    1. colorful vinyl pennants spaced and sized to meet competitive swimming requirements; generally placed five yards (short course) or five meters (long course) from the end of the pool
    2. enables backstroke swimmers to execute a backstroke turn more efficiently by counting their strokes
  • Finals

    championship heat of an event in which the top six or eight swimmers from the preliminaries compete

  • Failed Swim

    where a meet calls for proof of a time standard and the swimmer fails to meet that standard in a particular race

  • False Start

    swimmer moving before the start of a race

Back to Top


  • gold

    very soft ductile material that is noted for its resistance to corrosive metals; it is used primarily as a coating or plating

  • ground

    conducting connection between an electrical circuit and the earth or other large conducting body, thus making a complete electrical circuit

  • ground, earth

    portion of a circuit that is connected to a buried metallic object such as a grounding rod or water pipe

  • Gelcoat

    colored polyester-resin liquid applied to a mold during the manufacturing of fiberglass pool or spa shells

  • GPD

    gallons per day

  • GPH

    gallons per hour

  • GPM

    gallons per minute


    1. also called hand rail
    2. tubular steel or plastic device that can be gripped by swimmers or bathers for the purpose of steadying themselves; usually located near the steps in the pool

    condition caused by too much copper, not chlorine in the pool water; copper may get into the water by the bad practice of placing trichlor tabs in the skimmer; this acidic product will cause low-pH water, which in turn will dissolve metals in the equipment; the dissolved metal (usually copper) then stains hair, fingernails and, eventually, pool walls; keeping the pH too low or misusing acid can also cause it


    interrupts (de-energizes) the electrical circuit whenever it detects the presence of excess electrical current going to ground (usually 1/40th of a second and 5/1000th of an ampere)

  • Gunite

    concrete and sand mixture sprayed onto a reinforced steel form to create a pool shell; dry mixture of cement and sand is mixed with water at the "gun or spraying device", hence the name


    1. overflow trough at the edge of the pool through which floating debris, oil and other "lighter-than-weight" items flow; pools with gutters usually do not have skimmers
    2. also called a perimeter or recirculation system

    electronic valve in the pool heater that directs gas flow from the meter to the pilot and the burner tray

  • Gutter

    overflow trough at pool edge; also called a perimeter or recirculation system

Back to Top


  • Hypochlorite

    inorganic un-stabilized family of chlorine compounds used in various forms to provide chlorine for pool water; includes calcium hypochlorite, lithium hypochlorite and sodium hypochlorite

  • Hypochlorinator

    feeder device that applies chlorine solutions to pool water at a controlled rate

  • Hypobromous Acid (HOBr)

    most effective form of bromine in water for disinfecting

  • Hypochlorous ACID (HOCI)

    active sanitizing form of chlorine


    chemical elements either individually or collectively that constitute Group VIIB of the Periodic Table of Elements

  • Hydroxyl Ion (OH-)

    1. negatively charged particle of one oxygen and one hydrogen atom also called hydroxide
    2. contributes to pH balance

    unstable, colorless, heavy liquid used as an oxidizing agent in pools and spas; may also be used to dechlorinate pool or spa water

  • Hydrogen Ion

    positively charged nucleus of a hydrogen atom, which contributes to the acidity of pool water


    1. lightest chemical element
    2. component of water
    3. frequent product of many chemical reactions; pH is a measure of hydrogen in its ionic form in water
  • Hydrochloric Acid (HCI)

    1. strong acid used to control pH in pools and to acid wash pool interiors
    2. also called muriatic acid

    chemical compound used to kill or control plant growth or algae


    1. amount of calcium and magnesium dissolved in the water
    2. "water" or "total" hardness refers to the total magnesium and calcium dissolved in the water; calcium hardness refers to just the calcium
    3. measured by a test kit and expressed as ppm; proper range is 200 to 400 ppm

    1. water that is high in calcium hardness and other salts
    2. resists soap being lathered

    work done per unit of time; 1 horsepower equals 33,000 foot-pounds of work per minute or approximately 746 watts; motors for pumps are rated in horsepower

  • Hydrotherapy Spa

    unit primarily for therapeutic use to ease stress, muscle strains and other physical problems


    fitting(s) installed in the floor of the pool designed to manually or automatically release hydrostatic pressure beneath the pool by allowing ground water into the pool


    force involving built up ground water, which creates upward pressure beneath the pool shell


    fitting in the pool or spa on the water return line from the equipment that blends or mixes air and water, creating a high-velocity, turbulent stream of air-enriched water

  • Hot Tub

    a circular, wooden vessel with the sides and bottom formed separately and joined together by hoops, bands or rods; filled with heated and circulated water


    fossil-fueled, electric or solar device used to heat the water of a pool, spa or hot tub


    using a cooling coil, it removes heat from the air while the condenser coil transfers it to the water being cycled through the pump


    1. device located inside the heater providing for the transfer of heat from the heat source to the water; this is usually a series of metallic tubes with fins located just above the flames
    2. set of 8 or 10 ribbed copper tubes that absorb the heat produced below it and transfer it to the water cycling through its tubes

    screen attached to a frame which is then attached to a telepole used to remove large floating debris, such as leaves and bugs, from the water’s surface


    see grab rail


    see prelim

Back to Top



    water-sanitation device that uses electricity to generate metal ions, which are dispersed in the water; it works by passing a low-voltage DC current through a set of metallic (usually copper and silver) electrodes placed in line with the circulation equipment; copper is an algaecide, while silver is a bactericide; does not remove swimmer waste

  • IRON

    usually introduced into the water from iron plumbing or from well water, ferric iron can stain surfaces, while ferrous iron will turn your water a clear green color


    1. also called stabilized chlorine and chlorinated
    2. family of chlorine pool sanitizers that contain conditioner (cyanuric acid or isocyanuris acid) to protect the chlorine from the degrading UV rays in sunlight; the most common types are sodium dichlor and trichlor; the granular form is dichlor, which is fast dissolving and can be used for regular chlorination or superchlorination by broad casing into the pool or spa; tablet or stick form is trichlot (which is usually used in a chlorine feeder – either the floating type or the in-line erosion type) used for regular chlorination only
  • input voltage

    designed power source requirement needed by equipment in order to operate properly

  • inrush

    initial surge of current through a load when power is first applied; lamp loads, inductive motors, solenoids, and capacitive load types all have inrush or surge currents higher than the normal running or steady state currents; resistive loads such as heater elements, have no inrush

  • Interlock

    1. system of multiple doors with controlled interaction
    2. also known as lighttraps, airtraps, mantraps, and sallyports
  • intermittent duty solenoid

    solenoid designed to be energized for short periods; continuous operation may damage an intermittent duty solenoid

  • Influent

    1. water flowing into a filter, pipe, pool, chemical feeder or other space; water going into the pump is called in influent, while water leaving the pump is called the effluent
    2. the water coming into and up to the impeller from the suction lines; these pipes are under vacuum pressure
  • In-ground pools

    are partially or completely installed in the ground


    fitting in the pool or spa on the water return line from the equipment that water returns to the pool


    rotating member of a pump; its action creates the flow of water

  • IM

    1. individual medley
    2. event in which the swimmer uses all four strokes in the following order
Back to Top



    brand name of a three-way valve, which has simplified pool plumbing


    used in spas to provide additional thrust into the hydrotherapy jets

Back to Top



    1. dry, granular chlorinating compound with an available chlorine content of 35 percent;
    2. rapid-dissolving
    3. used to superchlorinate vinyl-liner pools, painted pools or fiberglass pools as well as spas and hot tubs
  • Liquid Chlorine

    1. sodium hypochlorite (NaOCI) solutions
    2. pool disinfectant
  • Liquid Acid

    see muriatic acid


    see saturation index

  • line voltage

    voltage existing in a main cable or circuit, such as at a wall outlet

  • line drop

    voltage loss occurring between any two points in a power or transmission line; such loss is due to resistance, reactance, or leakage of the line

  • line supervision

    electrical supervision of a wire run to detect tampering (a cut or shorted wire); usually requires a terminating element at end of monitored wire loop

  • load

    any device that consumes electrical power; the amount of power required for operation of a circuit or motion is obtained that moves the bolt

  • load rating

    control specification outlining the type of load, minimum and maximum currents, and the voltage

  • local alarm

    visual or audible signaling device located at monitored door, window, or other opening

  • lock status sensor (LSS)

    relay type to operate the LED with an SPDT switch to indicate low voltage and tampering of the lock face locally or to a remote monitoring location

  • line cord

    cord, terminating in a plug at one end used to connect equipment or appliances to a power outlet

  • lighttrap

    see interlock

  • light emitting diode (LED)

    diode, solid-state device that gives off virtually heatless colored light when electric current is passed through it; LEDs are very efficient, long lasting and are often used for digital readouts and annunciators; common colors include red, green, and amber

  • LOAD

    electric device, which consumes energy, placing a load on the source

  • Lumina System


    1. influent fitting, typically low on the wall in the deep end of a vinyl liner pool
    2. a cheaper alternative to a main drain

    see underdrain


    area in a pool or spa that house the underwater light

  • Leisure Surfacing


    device that attaches to a telepole and a garden hose; pressure from the garden hose creates a suction by which leaves and large debris are sucked into a large mesh bag

  • Leaching

    process of extracting a mineral from plaster pool interiors or tannic acid from wooden hot tubs


    1. elongated, capped plastic nibs at the bottom of a sand filter, which are slotted to allow for water passage while keeping the sand in the filter tank
    2. see also underdrain

    rubber caps or inserts that protect the pool plaster or vinyl liner from the sharp steel ends of the ladder


    structure used for getting in and out of the pool; a double-access ladder straddles the pool wall of an aboveground pool; an in-pool ladder is located in the pool only

  • Lane Rope

    floating markers attached to a line that stretches from the starting end to the turning end of the pool to separate each lane

  • lane line

    a rope with buoys that extends across the pool is to section off the water into long straight "lanes" so that swimmers do not bump into one another

  • Lane

    specific area in which the swimmer is assigned to swim

  • Lap Counter

    1. set of plastic display numbers used to keep track of laps during a distance race
    2. the person who counts for the swimmer stationed at the opposite end from the start
  • Lap swimming

    designated time when swimmers may use the distance of the pool at their own pace

  • Leg

    part of a relay event swum by one individual swimmer

  • Lifeline

    rope line across a pool to designate a change in slope in the pool bottom, or the beginning of deep water; usually supported by regularly spaced floats

  • Long Course

    pool 50 meters in length

  • Long Distance

    1. any freestyle event over 1500 meters, normally conducted in a natural body of water, such as a lake, river or ocean
    2. also known as marathon swimming
  • LSC

    1. Local Swimming Committee
    2. governing body for swimming on a local level
Back to Top



    the liquid dilution of hydrochloric acid used to lower pH and alkalinity, and to remove mineral stains and scale; extremely caustic and corrosive


    tiny, living, breathing creature in your pool; the purpose of disinfectants is to remove such pathogenic (disease causing) organisms


    any substance that is neither animal nor vegetable; such as calcium, manganese, magnesium, nickel, copper, silver, iron, cobalt or aluminum; their presence in high non-chelated concentrations can lead to stains and scale when conditions are right


    1. measure of the amount of magnesium dissolved in the water; part of total or water hardness
    2. causes scale if levels are too high
  • make

    to close or establish an electrical circuit

  • mother board

    master printed circuit board used to interface activities of individual printed circuit boards and the devices being controlled or monitored; the mother board is usually located at the back of a control panel assembly; individual printed circuit boards plug into it

  • monitoring loop

    continuous loop of wire starting at the control panel and running through switches in a system to indicate a breach of security through an open switch or a cut wire

  • momentary switch

    spring-loaded contact that, when pressed, closes two contacts; when pressure is removed, contacts open

  • momentary loss of power

    short interruption of power to the total equipment

  • momentary duty lock

    electric lock equipped with a solenoid that is energized only momentarily

  • mode of operation

    specified operational condition of a switch, lock, door system, etc.

  • millisecond

    one one-thousandth (0.001) of a second

  • milliampere

    one one-thousandth (0.001) of an ampere

  • maximum rating

    absolute maximum condition in which a device is designed to operate; voltage, frequency, current, temperature, humidity, shock, and other parameters can be specified as maximum

  • mantrap

    see interlock

  • maintained contact switch

    switch designed for applications requiring sustained contact, but with provision for resting


    1. 4 or 6 position valve combining the functionality of several valves into one unit, revolutionizing pool plumbing
    2. also called a rotary-type backwash valve; water from the pump can be diverted for various functions by merely turning the valve handle; the water may be sent to waste, used for backwashing, bypassing the filter for maximum circulation, for normal filtration, filtering to waste (rinse), or the valve may be closed to not pass water; the pump must be off before changing a valve setting
  • Movable Bulkhead

    a movable end wall that allows multipurpose usage


    1. machine for converting electrical energy into mechanical energy
    2. known as the dry end of the filter pump; it drives the impeller, which moves the water
  • Modular System

    cellular hi-rate sand filtration system utilizing an expandable modular cell design for increased flow rates


    1. unit of length equal to 1 millionth of a meter
    2. used to describe the pore size of filter media; (sand filters have openings of 25 to 30 microns; cartridge filters have openings of 8 to 10 microns; and D.E. (diatomaceous earth) filters have openings of 1 to 5 microns); a granule of table salt is between 90 to 110 microns
  • Membranes

  • Mechanical Systems

    integrated equipment including filters, piping, valves, pumps, disinfecting units and automatic control systems


    1. seal behind the impeller that prevents water from running out along the shaft of a motor
    2. also called a pump seal

    originally a brand name for a white plaster finish coat from 1/8-1/2-inch inch thick applied over the gunite or shotcrete


    branch pipe arrangement that connects several input pipes into one chamber or one chamber into several output pipes; a filter manifold connects several input pipes from the filter sept back into one common pipe


    see drain

  • masters swimming

    structured and supervised swimming period, where groups of adults participate in a set program; techniques and drills are utilized to improve performance

  • Middle Distance

    events 200-400 yards/meter in length

  • Meet

    equivalent to a "game"

Back to Top



    single oxygen atom, not yet bonded to anything; extremely powerful oxidizer when harnessed


    chemical used to make chlorine or bromine harmless


    gas that causes algae to bloom and disables chlorine


    1. class of chemical compounds used to oxidize or shock the water (destroy ammonia, nitrogen and swimmer waste); they contain no chlorine or bromine and do not kill living organisms; swimmers may re-enter the water in only 15 minutes after adding a non-chlorine shock
    2. granular form of potassium permonosulfate, used to oxidize materials such as microorganisms, contaminants or chloramines
  • National Electrical Manufacturers Association (NEMA)

    organization known for its standardization of wire and cable specifications

  • noise

    unwanted and/or unintelligible signals picked up on a cable circuit

  • normally closed (NC)

  • normally open (NO)

  • National Electrical Code (NEC)


    brand name for a thermoplastic resin used in the manufacture of certain pump components and various other pool equipment fittings

  • Negative Split

    swimming the second half of the race equal to or faster than the first half

  • National Age Group Time Standard

    1. time standards derived from the previous years’ results; broken down by age and sex as well as B, A, AA, AAA, AAAA divisions; these designations are and may be used for qualifying purposes; many LSCs have their own time standards
  • National Age Group Top 16

    time standards set for both short and long course based on previous years’ achievements; only times meeting these standards may be submitted for consideration each year

Back to Top


  • Orthotolidine (OTO)

    see DPD


    incorrect term used to describe water that is acidic or water that has a pH lower than 7.2


    1. also called a diffuser or distributor
    2. internal sand filter device that evenly distributes influent pool water over the sand filter bed
  • Oxidation

    1. chemical process for removing irritating organic compounds from pool water;
    2. rusting or corrosion process that occurs as metals weathers
  • Oxidizers

    agent that helps eliminate organic waste from pool water


    gaseous molecule comprised of three atoms of oxygen; it is generated on-site from air or oxygen and used for oxidation of water contaminants


    molecule containing three atoms of oxygen; known to be a very powerful sanitizer; ozone producing equipment creates this molecule by UV radiation or corona discharge generators

  • Organic Chlorine

    1. form of chlorine that contains carbon and hydrogen atoms
    2. most common ones for pool use are sodium dichloroisocyanurate (also know as sodium dichlorostriazinetrione) in granular form and trichloroisocyanurate (also known as trichlorostriazinetrione) in compressed form
  • Ohms Law

    In electrical systems, there is a relationship between current, voltage, and resistance. This is known as ohms law, and can be written in many different forms, but always boils down to V=IR, where V is voltage, I is current, and R is resistance.

  • operating voltage

    1. voltage by which a system operates
    2. nominal voltage with a specified tolerance applied; design voltage range necessary to remain within the operating tolerances; for example, for a system specified 120 volts +/-10 percent of nominal, 120 volts is the nominal voltage and the design voltage range is 108 to 132 volts AC
  • output voltage

    designed power source produced by a power supply

  • On-ground pools

    see above ground pools

  • ORP

    1. exudation reduction potential
    2. measurement of a body of water’s ability to oxidize contaminants; measured with an electrode and an electronic meter
    3. an indication of the sanitizing level or degree of safety from disease in the water; measured in millivolts with the accepted minimum level being 650 mV (millivolt)
  • Official

    a judge on the deck of the pool at a sanctioned competition who is there to enforce rules; there are stroke and turn judges, administrative officials, starters, timers and referees

  • open swimming

    see recreational swimming

  • open water swimming

    an organized swim event in the ocean, lake or river; distances tend to be longer

Back to Top


  • Precipitate

    solid particles forced out of solution by a chemical reaction; they may settle to the bottom of the pool or remain suspended in the water

  • ppm

    1. parts per million
    2. unit of measurement used in chemical application; it indicates the amount, by weight of a chemical, in relation to one million parts by weight of water (examples
  • POTASSIUM Peroxymonosulfate

    1. active ingredient and chemical name of a non-chlorine shock treatment or non-chlorine oxidizer
    2. does not kill bacteria or algae, but it will oxidize or destroy ammonia, nitrogen and swimmer waste;
    3. it has a low pH
    4. does not increase chlorine or bromine levels the way that superchlorination does
    5. reactivates bromine to its killing form, hypobromous acid

    1. substance made of giant molecules formed by the union of simpler molecules; many water clarifiers are made from organic polymers; an example would be polymerized ethylene, called polyethylene
    2. algaecide/algaestat made up of repeating polymer molecules; used for green algae and available in varying strengths

    see non-chlorine shock


    chemical reagent dye used to test for pH; it can measure pH from 6.8 to 8.4

  • pH

    indicates the acidity or alkalinity of pool water; on a scale of 0 to 14, values below 7 are acidic, while values above 7 are alkaline; ideal pool pH is a reading of 7.4 – 7.6

  • printed circuit board

    means of making electrical interconnections without using insulated wires; printed circuit boards provide a supporting and insulating medium for components and conductors in a form that is readily adaptable to machine assembly

  • potentiometer (pot)

    variable resistor

  • primary

    transformer winding that receives the energy from a supply circuit


  • Pump

    motor-powered mechanical device that creates pressure and water flow to permit filtration, heating and water circulation; pools usually use a centrifugal-type pump

  • PVC

    1. polyvinyl chloride
    2. used to make flexible and rigid PVC pipe

    two-position valve used for backwashing sand or DE filters

  • Pump Strainer

    lint and hair trap on the suction side of the pump to remove debris with a minimum of water flow restriction


    1. also called a pump performance curve
    2. graph that represents a pump’s water flow capacity at any given resistance

    volume of liquid a pump is capable of moving during a specified period of time; usually gallons per minute (gpm)

  • Psi

    pounds per square inch


    used in pool heaters that opens when the flow rate is insufficient for safe heater operation; this disrupts the circuit in the heater, preventing it from firing


    1. return side of the plumbing
    2. section from the pump impeller toward the pool

    device indicating pressure in a filter system

  • Pressure Differential

    difference in the amount of water pressure being exerted on two parts of a hydraulic system, such as the incoming vs. the outgoing water through a filter


    1. test for the rate of water flow
    2. a test for leaks in plumbing by placing a line in question under pressure and waiting for the pressure to drop

    depositing diatomaceous earth (D.E.) onto the filter grids or elements


    sliding disc assembly that changes valve position in a push-pull valve


    mixture of white cement and white marble dust used as an interior finish, which can be tinted and colored applied to gunite or shotcrete pools or spas


    manually operated faucet or valve for draining liquids or releasing air pressure; air-relief valve on a filter is an example

  • Permanent Medium Filter

    uses sand or other medium that does not require replacement

  • Perimeter System

    see recirculating system


    organism that causes disease

  • Pace Clock

    large clock with a large second hand and a smaller minute hand, used to check pace or to maintain intervals in practice; may also be digital

  • Proof of Time

    a requirement at some meets to make certain that all swimmers have legally met time standards for that meet

  • Prelims

    1. preliminaries, also called heats or trial
    2. races in which swimmers qualify for the championship and consolation finals in events
Back to Top



    chemical compounds of ammonia used as algaecide and algaestats


    see quaternary ammonium compound

  • Q-Time

    qualifying time necessary to compete in a particular event and/or competition

Back to Top



    condition preventing full flow of water; restriction on the suction side creates higher vacuum, (or suction) while on the pressure side creates higher pressure


    1. amount of measurable chlorine remaining after treating the water with chlorine
    2. amount of chlorine left in the pool or spa water after the chlorine demand has been satisfied

    amount of measurable bromine remaining after treating the water with bromine

  • Recirculate

    this setting bypasses the filter, water coming into the multiport does a U-turn and heads back towards the pool; used only when the filter is broken or when adding specialty chemicals, which specify using this setting


    1. reinforcement bar
    2. used to add strength to a concrete; after excavation of an in ground pool, a steel cage is formed out of re-bar, and the gunite shell is shot over and surrounding it

    chemical agents, dyes, indicators or titrants used in testing water balance

  • regulated power supply

    power supply that provides a constant output regardless of input voltage variations

  • resistor

    circuit element whose chief purpose is to oppose the flow of current

  • resistance

    1. opposition to flow of an electric current (measured in ohms)
    2. reciprocal of conductance
  • reset time

    time required to return the output to its original condition

  • remote reset

    switch located at a monitored opening; if a violation occurs, the alarm at the main control console cannot be turned off until the door is secured and the remote reset is activated; its purpose is to ensure the inspection of an opening that has been violated or left open

  • remote alarm

    visual or audible signaling device used to signal violations at locations removed from the central control station or monitored openings; for example, a remote alarm may be placed on a roof, or at guard stations outside a building

  • relay

    electrically controlled-device that opens and closes electrical contacts to effect the operation of other devices in the same or another electrical circuit

  • recycle time

  • rectifier

    solid state electrical device that will allow current to flow in one direction only; it is designed to convert alternating current to direct current

  • rated voltage

    maximum voltage at which electric component can operate for extended periods without undue degradation or safety hazard

  • reverse circulation

    pool-water circulation system; water is taken from the surface of the pool and returned through inlets at the bottom of the pool

  • Residential

    pools for home use rather than for public or commercial use


    .. A horizontal slot, formed or cut in a concrete, tile, masonry or block wall into which the top edge of Natatec PVC membrane or NataDek flooring or other material can be inserted and anchored.

  • Recreational Surfacing

  • Recirculating System

    1. system of pipes, pumps, filters that allows water to be taken from the pool, filtered, treated and returned to the pool
    2. also called a gutter or perimeter system

    quantity of water flowing past a designated point within a specified time period, measured in gallons per minute (gpm)

  • Recreational swim team

    swim team run by a club, or municipality or county

  • Relay

    an event in which four swimmers compete together as a team to achieve one time

  • Referee

    1. official who has the authority over all other officials at a meet
    2. makes all final decisions and sees to the efficient running of the meet
  • Recreational swimming

    1. also called open swimming
    2. set time when swimmers of all ages may come to the pool; no lane lines are in the water; the water is "open"
Back to Top


  • sistema de visión

    technology, which isolates nascent oxygen into a powerful sanitizing tool

  • Sodium Thiosulfate

    1. chemical used to prevent false pH readings
    2. added to the water sample to remove chlorine prior to testing
  • Sodium Sesquicarbonate

    1. chemical mixture of equal parts soda ash and sodium bicarbonate used to increase pH and total alkalinity in pool and spa water
    2. has a pH of 10.1

    chemical used to neutralize or de-chlorinate pool and spa water


    new technology that renders algae incapable of processing carbon dioxide, which they need to live


    see soda ash


    water that contains less than 100 ppm of calcium and magnesium; pools and spas should never be filled with soft water from a softener; water with less than 100 ppm of hardness should be increased to a minimum of 150-200 ppm using calcium chloride


    see cyanuric acid


    1. discoloration or a colored deposit on the walls or bottom of a swimming pool or spa; most often, stains are metals, such as iron, copper and manganese; may appear as green, gray, brown or black; may discolor the water; sometimes a sequestering agent or chelating agent will remove them; if not, usually an acid wash is necessary to remove them from the walls and bottom
    2. stains are sometimes confused with scale

    see chelate


    second line of defense is a basket at the pump; holes are smaller than those in a skimmer basket, and prevent the pump impeller from clogging


    see isocyanurates


    1. plumbing prior to and carrying water to the pump
    2. under vacuum pressure
  • Super Chlorination

    see shock treatment and breakpoint chlorination


    1. soluble chemical compound that reduces the surface tension between two liquids
    2. used in many detergents and soapy cleaning compounds

    practice of adding significant amounts of an oxidizing chemical (usually non chlorine oxidizers, such as sodium persulfate or potassium peroxymonosulfate) to the water to destroy ammonia and nitrogen compounds or swimmer waste


    1. describes the products used in shocking, such as hypochlorites, potassium permonysulfate or hydrogen peroxide
    2. act of bringing the sanitizer level up so high that breakpoint chlorination is reached; when breakpoint is reached, a "shock" is sent through the water, tearing apart molecules and slashing through cell walls
  • Sequestering Agent

    see chelant


    solid material settled out from the water

  • SCUM

    1. extraneous or foreign matter, which rises to the surface of the water and forms a layer or a film
    2. residue deposited on the tile or walls of the pool or spa
  • Scale

    see calcium carbonate

  • Saturation Index

    1. developed by Mr. Langelier
    2. a numerical value used to indicate whether pool water is out of balance (either scale-forming or corrosive); four factors are taken into account

    chemical agent used to remove unwanted contaminants


    to kill all living things, including bacteria and algae


    see soda ash

  • Shock Treatment

    extra large dose of chlorine applied every two weeks or as needed to kill algae and eliminate chloramines in the water


    1. sodium carbonate (Na2CO3)
    2. chemical used to counteract an acidic condition by raising pH
  • Sodium Bicarbonate (NaHCO3)

    pool additive (baking soda) used to raise total alkalinity


    see dry acid

  • Sodium Dichloroisocyanurate Na(C3N3O3Cl2)

    1. granular organic chlorine that contains 62 percent available chlorine
    2. also known as sodium dichloro-s-triazinetrione

    see dichlor

  • Sodium Hypochlorite (NaOCI)

    1. inorganic chlorine in clear, liquid form
    2. provides 10 percent to 12 percent available chlorine; has a pH of 13 and requires that small amounts of acid be added to the pool to neutralize the high pH
    3. does not contain conditioner or stabilizer to protect it from sunlight, but it is protected if stabilizer or conditioner is already in the water

    1. active ingredient and chemical name of a non-chlorine shock treatment or non-chlorine oxidizer
    2. does not kill bacteria or algae, but it will oxidize or destroy ammonia, nitrogen and swimmer waster
    3. does not increase chlorine or bromine levels the way that superchlorination does, so water may be entered in 15 minutes after addition
    4. will not reactivate bromine
  • single pole, single throw (SPST)

    switch with only one moving and one stationary contact, available either normally open (NO) or normally closed (NC)

  • switch, normally open

    see normally opened

  • switch, normally closed

    see normally closed

  • switch, momentary

    see momentary switch

  • switch, maintained

    switch that, when activated, maintains its activated position until it is inactivated

  • switches

    devices that make or break connections in an electrical or electronic circuit; switches are usually manually operated but can also work by mechanical, thermal, electromechanical, barometric, hydraulic, or gravitational means

  • spike

    momentary increase in electrical current; spikes can damage electronic equipment

  • solenoid

    1. electromechanical device that operates the lockbolt
    2. when electricity is applied, a mechanical device
  • single pole, double throw (SPDT)

    switch or relay contact form (1 form C) that has a normally open and a normally closed contact with a common connection

  • short

  • security interlock

    multidoor system in which all doors are normally closed and locked; releasing one door disables the releases for all other doors until the first door is closed and relocked

  • security condition sensor (SCS)

    sensitive crystal relay to operate the LED with an SPDT switch to indicate low voltage and tampering of the lock face locally or to a remote monitoring location; primarily used in higher security applications

  • secondary

    transformer winding that receives energy by electromagnetic induction from primary

  • Sally ports

    see interlock


    1. part of a skimmer that adjusts automatically to small changes in water level to assure a continuous flow of water to the skimmer; the small floating "door" on the side of the skimmer that faces the water
    2. the weir also prevents debris from floating back into the pool when the pump shuts off
  • SILT

    soil particles having diameters between 0.004 and 0.062 mm

  • Skimmer


    removable, slotted basket or strainer placed in the skimmer on the suction side of the pump; beneath the lid, the basket strains debris, as the first line of defense in filtering the water


    attached to a telescopic pole, a leaf rake is a very useful tool in keeping the pool clean


    water or a liquid containing a high concentration of suspended solids

  • Solar Heating System

    panels or coils of plastic or metal through which water passes to increase the temperature from the sun’s heat


    black mats of miniature plastic tubes through which water is pumped, absorbing the heat as it passes through; these mats are roof mounted with up and down plumbing connecting it


    see make-up water

  • SPA

    filtered, hot water vessel with hydrotherapy jets and air induction; can be portable or installed permanently


    1. also called diving board
    2. recreational mechanism for entering a swimming pool consisting of a semi-rigid board that derives its spring from a fulcrum mounted below the board and attached to the deck
  • SPS Systems


    device in a perimeter gutter system that controls the amount of water coming into the gutter from the weir openings in the face of the gutter


    1. large tank constructed near or immediately adjacent to the edge of the pool that incorporates a modulating valve on the main drain to maintain a normal operating level well below the level of the pool in quiescent operation
    2. the difference between the pool level and the operating level in the surge tank is the surge capacity, which is normally required to be approximately 1 to 2 gallons per square foot of pool surface area

    1. part of a stainless steel gutter that controls the operating level of the pool at quiescent (low or no-use periods) to ensure that adequate in-pool surge is available when swimmers enter the pool
    2. eliminate the need for a surge control tank

    insoluble solid particles that either float on the surface or are in suspension in the water, causing turbidity

  • Swimmer Load

    the number of persons in the pool area at any given moment, or any stated period of time


    the origination of electrical power; the source for a filter pump (load) is probably a timer clock

  • SAND

    usually refers to the filter medium used by a sand filter; the grade most often specified by filter manufacturers is grade No. 20 with a particle size of 45 to 55 mm


    filter using sand or sand and gravel as the filter medium; the pump diffuses water over the top of the sand bed, and forces it through the sand and into the laterals on the bottom


    portion of the filter element consisting of cloth, wire screen or other porous material on which the filter medium or filter aid is deposited; the nylon grid on a D.E. filter is the septum


    mixture of sand and cement sprayed onto contoured and supported surfaces to build a pool or spa; plaster is applied over the shotcrete; shotcrete is premixed and pumped wet to the construction site

  • synchronized swimming

  • Stroke & Turn Judge

  • Streamline

    position used to gain maximum distance during a start and/or push off from the wall in which the swimmer’s body is as tight as it can be

  • Starter

    the official at a meet responsible for starting each heat and calling the next heat to the blocks

  • Scratch

    to withdraw from an event

  • Sprint

    1. describes the shorter events (50 and 100)
    2. in training, to swim as fast as possible for a short distance
  • Split

    1. swimmer’s intermediate time in a race; splits are registered every 50 yards or meters and are used to determine if a swimmer is on record pace
    2. under certain conditions, splits may also be used as official times
  • Short Course

    a pool 25 yards or 25 meters in length

  • Set

    combined group of drills to form a complete practice

  • Senior Swimming

    program which provides fair and open competition in national swimming championships; it is designed to afford maximum opportunity for participation, provide an educational experience, enhance physical and mental conditioning and develop a pool of talented athletes for international competition; there are no age restrictions in senior competition

  • Seeding Times

    time a swimmer uses to enter a meet; this time, which is written on the entry card, determines ones position and lane in a particular meet

  • Seed

    to distribute the swimmers among the heats and lanes according to their times; in most cases, the fastest swimmers are in the final heat of an event

Back to Top



    cloudy condition of the water due to the presence of extremely fine particles in suspension that cannot be trapped by the filter because they are too small; adding a clarifier, such as an organic polymer or alum, will coagulate the particles and make the filter more efficient

  • Trichloroisocyanurate (C3N3O3Cl3)

    1. organic chlorine available in compressed tablets or sticks, containing 90 percent available chlorine
    2. also known as trichloro-s-triazinetrione

    1. slow-dissolving, tableted or granular, stabilized organic chlorine compound providing 90 percent available chlorine
    2. used for regular chlorination but must be dispensed using a floating feeder or an in-line feeder (chlorinator)
    3. contains an ingredient (cyanuric acid or stabilizer) that prevents the chlorine from being destroyed by the ultraviolet (UV) rays of the sun
    4. pH of 2.8, and regular trichlor tabs should not be placed in the skimmer, as the low pH will corrode the metal components in the equipment
  • Total Dissolved Solids

    1. measure of the total amount of dissolved material in the water; maximum amount in pools is 2500 ppm, maximum in spas is 1500 over starting TDS; the only way to effectively lower TDS is to drain part or all of the water and replace it
    2. also called TDS

    total amount of chlorine in the water; includes both free available and combined chlorine

  • Total Alkalinity

    1. amount of alkaline bicarbonate in pool water
    2. acts as a buffer to prevent fluctuations in pH

    see tannin

  • Titration


    small plastic strips with pads attached that have been impregnated with reagents that can be used to test pool water for residuals, levels, constituents or demands; usually dipped in the water, and the resulting colors of the pads are compared to a standard set of colors to determine concentration


    1. apparatus or device used to monitor specific chemical residuals, levels, constituents or demands in pool or spa water; kits usually contain reagents, vials, titrants, color comparators and other materials needed to perform tests; the most common pool and spa water tests are
  • TDS

  • Tannin

    1. harmless organic chemical that is leached out of new redwood or cedar hot tubs and is present in some source water
    2. also called tannic acid
  • transient voltage

    1. refers to several parameters of a transient
  • transient

    any increase or decrease in the excursion of voltage, current, power, heat and so forth, above or below a nominal value that is not normal to the source

  • transformer

    1. electric device that changes voltage in direct proportion to currents and in inverse proportion to the ratio of the number of turns of its primary and secondary windings
    2. see primary and secondary

    1. also called turnover rate
    2. number of times a quantity of water equal to the total capacity of the pool passes through the filters in a stated time; usually in turnovers per day; pool capacity in gallons, divided by pump flow rate in gallons per minute (gpm), divided by 60 minutes in 1 hour, will give hours for 1 turnover

    mechanical or electrical device that automatically controls the periods that a pump, filter, heater, blower, automatic pool cleaner or other electrical devices are on or off


    long-handled aluminum pole, which extends in length to which various pool-cleaning tools, such as brushes or vacuums, can be attached

  • TEE

  • Taper

    final preparation phase prior to major competition; an older more experienced swimmer will shave his entire body to reduce resistance in the water

  • trial

    see prelims

  • Tri-Meet

    any competition between three clubs

  • Touch Pad

    large sensitive board at the end of each lane where a swimmer’s touch is registered and sent electronically to the timing system

  • Time Trial

    a time-only swim, not part of a regular meet

Back to Top



    using UV wavelength radiation to destroy contaminants in water; UV light is also used to create ozone molecules for the same purpose


    1. lower collection system in a filter, which directs filtered water back toward the pool
    2. distributes water in reverse during backwashing
    3. also called filter laterals or lower collection system

    fixture designed to illuminate a pool or spa from beneath the water’s surface

  • U.S. swim team

    age group program authorized by the U.S. Swimming organization

  • USA Card number

    unique number assigned to a swimmer when they join United States of America Swimming

  • USA Swimming

    1. United States of America Swimming, Inc.
    2. national governing body for amateur competitive swimming in the United States
Back to Top



    technology, which isolates nascent oxygen into a powerful sanitizing tool

  • volt (V)

    1. unit of electromotive force
    2. the difference of potential required to make a current of one ampere flow through a resistance of one ohm
  • voltage

    term most often used (in place of electromotive force, potential, potential difference, or voltage drop) to designate electrical pressure that exists between two points and is capable of producing a flow of current when a closed circuit is connected between the two points

  • voltage drop

    voltage loss experienced by electrical circuits due to two principal factors

  • volt/amp (VA) rating


    1. one of several types of suction devices designed to collect dirt from the bottom of the pool; some discharge dirt and water into the filters, some discharge to waste, and some collect debris in a porous container, allowing water to return to the pool; some are self-propelled; others must be pushed or pulled across the pool
    2. low-pressure condition created in the suction line
    3. cleaning process of sucking leaves, algae and debris from the pool floor

    device placed in the plumbing line, which restricts or obstructs water flow to create desired hydraulics, or may permit flow in one direction only


    1. fitting or device that consists of a tube constricted in the middle and flared on both ends; a fluid’s velocity will increase and a fluid’s pressure will decrease while passing through the constriction; placing a tube or pipe at the constriction point creates a vacuum; fluid or air can then be drawn in through the tube; a hydrotherapy jet draws air in and mixes it with the water using this principle
    2. increasing water velocity by restricting pipe size

Back to Top


  • watt

    common unit of electrical power; one watt is dissipated by a resistance of one ohm through which one ampere flows

  • wire

    slender rod or filament of drawn metal


    1. also called coagulant or flocculants
    2. a chemical compound used to gather (coagulate or agglomerate) or to precipitate suspended particles so vacuuming or filtration may remove them; there are two types
  • WEIR

    see skimmer weir

  • Winterizing

    procedure for protecting pools, spas and hot tubs from freezing conditions; includes physical and chemical protection


    1. also called coagulant or flocculants
    2. a chemical compound used to gather (coagulate or agglomerate) or to precipitate suspended particles so vacuuming or filtration may remove them; there are two types:  inorganic salts of aluminum (alum) and other metals, and water-soluble organic polyelectrolytes
  • WEIR

    see skimmer weir

  • Winterizing

    procedure for protecting pools, spas and hot tubs from freezing conditions; includes physical and chemical protection

  • Warm Down

    low intensity swimming used by swimmers after a race or main practice; it rids the body of excess lactic acid and gradually reduces heart rate and respiration

  • Warm Up

    used by a swimmer prior to a main practice, set or race; loosens and warms muscles and gradually increases heart rate and respiration

  • Water Aerobics

    see water exercise

  • Water Ballet

    see synchronized swimming

  • water exercise

    1. also called water aerobics
    2. an exercise routine in the water
  • Water polo

    high endurance sport with soccer-like strategy played in the pool; forward, backs and goalies try to throw a ball into the opponent’s net; players are not allowed to touch the bottom of the pool while playing

Back to Top


  • zone

    1. specific area of protection
    2. portion of a large protected area
    3. power supply to operate equipment
  • Zone

    1. specific area of protection
    2. portion of a large protected area
    3. power supply to operate equipment
Back to Top