A to Z Definitions of Common Swimming Pool Terms

Understanding the world of swimming pools doesn’t have to be daunting. We’ve created this concise glossary packed with essential swimming pool terms so that you can master pool maintenance, ownership, and lifestyle quickly and easily. Please note that all swimming pool definitions are taken from ANSI/NSPI standards courtesy of the Association of Pool & Spa Professionals. Dive in to discover everything there is to know about your swimming pool!

For questions related to swimming pool terms or pool liners, contact our pool experts today.



Having a pH below 7.0. Opposite of basic.


Adult Supervision

Supervision by a person of reasonable intelligence and ability, at least 18 years of age or, if younger, with training in supervision, such as a Red Cross Lifeguard.



Abbreviation for the alkalinity factor in calculating the saturation index of water.


Aggressive Water

Pool water that is corrosive because it is low in pH and/or calcium hardness and/or total alkalinity.



Microscopic, plantlike organisms that contain chlorophyll.


Algaecide (also spelled Algicide) 

Any chemical or material that kills algae.



Capable of killing algae.



Any substance or agent that inhibits the growth of algae.


Algistatic Able to inhibit the growth of algae.



Having a pH above 7.0.



A measure of the pH buffering capacity of water, generally expressed in terms of the equivalent concentration of calcium carbonate in milligrams per liter (or ppm).



A chemical compound of hydrogen and nitrogen that combines with free chlorine in pools to form chloramines, or combined chlorine. Also combines with free bromine to form bromamines.



Single-celled microorganisms of various forms, some of which cause infections or disease.



Any chemical that kills bacteria.



The process of cleansing the filter medium and/or elements by the reverse flow of water through the filter.


Backwash Cycle 

The time required to backwash the pool filter medium or elements and to remove debris in the filter vessel.


Backwash Rate 

The rate of flow water through the pool filter medium per unit of area (US gallons per minute per square foot).



In swimming pools, this refers to a condition of the water that is neither scaling nor corrosive.



A chemical used to raise the pH and/or total alkalinity of pool water.


Base Demand 

A measure of the amount of alkaline material required to raise the pH to a predetermined level. This can be accomplished by use of a base demand test, whereby a standard base is added by drops to the pH test solution until the desired pH is reached.



Having a pH above 7.0. Opposite of acidic.



Any person using a pool and adjoining deck area for the purpose of water sports, recreation, therapy, or related activities.


Bleach (Sodium Hypochlorite) 

Also called liquid chlorine. A chlorine source typically has between 5% and 16% available chlorine.



A salt that contains a bromide ion. Bromide becomes hypobromous acid when reacted with oxidizers such as chlorine, ozone, or monopersulfates.



One of several chemicals that yield hypobromous acid when added to water.



Any chemical that, when dissolved in water, will resist pH change. Also, any chemical solution used to calibrate pH instruments.


Calcium Hardness 

A measure of the amount of calcium dissolved in water, expressed in ppm of equivalent carbonate.


Caution(signal word) 

Indicates a potentially hazardous situation that, if not avoided, coulde result in minor or moderate injury.



Abbreviation for the calcium hardness factor in calculating the saturation index of water.



Abbreviation for cubic feet per minute.


Chemical Feeder 

A device (floating or mechanical) used to add a chemical to pool water.



A compound formed when chlorine combines with nitrogen-containing compounds such as perspiration and ammonia. These compounds can cause eye and skin irritation, have strong objectionable odors, and have very low sanitizing capability.



A device used to add or deliver chlorine disinfectant at a controllable rate. Chlorinators are designed for specific chlorine compounds and should be used with the compounds for which they are designed.



A chemical element that exists as a gas in its elemental form or as a chemical compound. Used as an oxidant and biocidal agent to disinfect pool water.


Chlorine Demand 

The amount of chlorine necessary to oxidize all organic matter present in pool water at any given moment or over a period of time.


Chlorine Residual 

The amount of available chlorine remaining in water after the chlorine demand has been satisfied.


Circulation System 

A system of mechanical equipment or components designed to ensure the even distribution of heat, chemicals, and filtration of water throughout a pool. Includes filters, heaters, pumps, chlorinators, piping, inlets, drains, skimmers, and other devices.



A chemical that coagulates and neutralizes suspended particles in water.



The degree of transparency of pool water. Characterized by the ease with which an object can be seen through a given depth of water.



A chemical, usually alum, used in pools to gather and precipitate suspended matter.



To collect, via a chemical compound, suspended matter in pool water.



An undesirable organic or inorganic, soluble or insoluble substance in water, including microbiological organisms. Examples: dirt, body oil, algae.



The cap on the wall that provides a finishing edge around a pool. It can be formed, cast in place, precast, or prefabricated from metal or plastic materials, brick or stone. It may be used as part of the system that secures a vinyl liner to the top of the pool wall.



The etching, pitting, or eating away of material.



The radius that joins the floor and wall of a pool.



Something that covers, protects, or shields a pool. Example: Solar Cover, Winter Cover.


Deep Area 

Water areas exceeding 5 feet in depth.



Any chemical used to kill undesirable or pathogenic (disease-causing) bacteria.



The conversion of liquid molecules into vapor.



A boundary between a pool area and the outside intended to deter unauthorized entry from outside. Not intended as a structural barrier to be sat, walked, or climbed on.



A vessel that removes undissolved particles from water, recirculating the water through a porous substance (a filter medium or elements).


Filter Cycle 

The operating time between cleaning or backwash cycles.


Filter Medium 

A finely graded material (such as sand) that removes solid particles from water.


Filter Sand 

A hard, silica-like substance free of carbonates or other foreign material and used as the medium in sand filters.



The process of capturing suspended particles and clarifying water.


Filtration Flow 

The design rate of flow, in volume over time (gallons per minute, gallons per hour), through the filter system when installed per the manufacturer’s instructions with a new, clean filter medium.


Filtration Rate 

The rate of water flowing through a filter during a given period of time, expressed in US gallons per minute per square foot of effective filter area.


Flocculant (floc) 

A chemical substance or compound that promotes the combination, agglomeration, or coagulation of suspended particles in water.


Free Available Chlorine 

The portion of total chlorine remaining in chlorinated water that is not combined with ammonia or nitrogen compounds and will react chemically with undesirable or pathogenic organisms. The most active disinfectant in pool water.


Hair and Lint Strainer 

A readily removable, perforated, or otherwise porous container used to catch coarse material.


Main Drain 

An outlet located at the bottom of a pool that conducts water to the recirculating pump.



A machine that converts electrical energy into mechanical energy. When electrical current is supplied to a series of wires (windings), a magnetic field is created that drives the rotor and shaft of a pump impeller.



An element introduced into the pool via perspiration, hair spray, cosmetics, etc. Easily combines with chlorine to form chloramines.



Products used to destroy organic water in water.



Disease-producing microorganisms.



A value for the relative acidity or basicity of a substance such as water, as indicated by the hydrogen ion concentration. Expressed on a scale of 0 to 14, 0 being the most acidic, 7 being neutral, and 14 being the most basic.



Abbreviation for parts per million, the unit of measurement used in chemical testing that indicates the parts by weight in relation to one million parts by weight of water. Essentially identical to the term milligrams per liter (mg/L).


Pressure Gauge 

A gauge that measures the amount of pressure built up within a closed container, such as a filter.


Pressure Switch 

A device that will not allow a heater to fire unless there is adequate water pressure in the system.



Abbreviation for pounds per square inch.



A mechanical device, usually powered by an electric motor, which causes hydraulic flow and pressure for the purpose of filtration, heating, and circulation of pool water.


PVC (polyvinyl chloride)

A thermoplastic resin commonly used for pool piping and plumbing components.


Rate Of Flow 

The quantity of water flowing past a designated point within a specified time, such as the number of gallons flowing in one minute (gpm).



Chlorine residual, or the amount of measurable chlorine that remains after treating water with chlorine.


Return Inlet 

The aperture or fitting through which the water under positive pressure return into a pool.



The practice of adding a sufficient amount of chlorinating compound to water to destroy chlorine demand compounds and any combined chlorine present. Generally, the level of chlorine added is 10 times the level of combined chlorine in the water.


Total Alkalinity 

The ability or capacity of water to resist change in pH is also known as the buffering capacity. Measured with a test kit and expressed as ppm.



A cloudy condition of water due to the presence of extremely fine particles in suspension that interfere with the passage of light.


Water Pressure Switch 

A switch that, from water flow, detects abnormally low pressures on a piece of equipment and can shut it off.



The process of preparing a pool or spa for freezing weather. Includes chemical treatment of the standing water plus physical and chemical protection against freezing of the pool and its equipment.


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