Quick reference dictionary of terms, definitions, and jargon

Glossary of Terms

Swimming Pools Terminology & Definitions

You might find this information valuable for a quick reference to the terminology widely used in the swimming pool industry, whether you are looking to buy a new pool or a pool owner looking for some information.


A manually-operated brass or plastic valve is located at the top of a filter tank to relieve the pressure inside the filter and remove the air inside the filter (bleeding the filter). Also known as a pressure-relief valve.

An above-ground pool is a typical round or oval-shaped structure that houses water and sits on top of the ground; above-ground pools do not require excavation and are generally quicker and cheaper than inground pool options.

One of two elements that determine the pH levels of your pool. Highly acidic water (low pH) can cause structural damage to both your pool and your pool equipment.

During the summer, algae can develop in the pool water. Algae are most commonly a collection of green micro-organisms that collect together in water – algae can heavily affect water clarity and make it unsuitable for swimming. Microscopic plant-like organisms that contain chlorophyll. Algae are nourished by carbon dioxide (CO2) and use sunlight to carry out photosynthesis. It can be introduced by rain or wind and grows in colonies, producing nuisance masses. Algae can harbor bacteria and can be slippery. There are thousands of known species of algae. The most common algae in pools are black, blue-green, green, and mustard (yellow or drawn).

After acid, alkali is the other main element, which determines the pH level of the pool. While very acidic water (low pH) can damage the pool, heavily alkaline water (high pH) can lead to calcium deposits and scale forming.

Chemical compounds are designed to kill, prevent and control algae growth in pool water.

A pool maintenance system that will agitate and/or vacuum debris from the pool interior automatically.

A heavy pool cover connected electronically or manually extends over the pool, protecting the pool from debris and temperature changes and adding an important safety measure.


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

If pool water is not properly disinfected, swimmers can contaminate it with bacteria. This can lead to the spread of waterborne diseases and illnesses.

The process of thoroughly cleaning the filter by reversing the water flow through it with the dirt and rinse water going to waste.

Also known as a sun shelf or tanning ledge, a Baja shelf is a shallow, expansive pool designed for lounging, tanning, and more.

Chemical compound designed to prevent corrosion and staining by balancing the pH, total alkalinity, and calcium hardness in pool water.

The interaction and measurement of different pool chemistry factors include pH, temperature, hardness, and total alkalinity.

Indoor, subterranean pools built in a converted basement of a home.

The capacity of the pool in terms of how many people can use it at once.

Base plates are parts of an above-ground pool that sit beneath each upright, providing a connection point for the base track and the upright itself.

A part of an above-ground swimming pool stretches from base plate to base plate between the uprights of the swimming pool and forms the bottom rim of the pool structure. During installation, this track has a groove into which the wall of the swimming pool is rolled.

Also known as a zero-entry pool, beach entries are slightly sloped gradual entrances that replace swimming pool steps, giving pools a natural, organic appearance.

Pools are designed according to an individual’s preferences and tastes in every way: from the size, shape, and style to finishes.

Boilers regulate the temperature of the pool water.

Submerged systems allow a pool to be divided into different sections with an automated raised wall.

A common term for bromide salt is used to supply bromide ions to the water to oxidize or change into hypobromous acid, the killing form of bromine. Used as a disinfectant.

A common name for a chemical compound containing bromine is used as a disinfectant to destroy bacteria and algae in swimming pools and spas. Available as a tablet or as sodium bromide, a granular salt.

Abbreviation for British Thermal Unit. The amount of heat necessary to raise 1 lb. of water 1 degree Fahrenheit.

A simple method of checking if there is water loss in the pool and the possible cause. The test involves filling a bucket with pool water, partially immersing it in the pool, and, after pausing pump operations, comparing the water levels in the pool with that in the bucket to see how great the water loss is. A significant difference could point to a leak in the pool.

Pool coping with rounded edges extends over the pool’s side used to finish exposed edges of decking.


A small tentlike poolside structure is used as a changing room or lounge area.

How much calcium carbonate is present in swimming pool water

Chlorine in powder form; used as pool shock

Style of coping where the pool deck extends to the edge of the pool and does not hang over like in bullnose coping styles

A 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.

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

A device that dispenses chemicals into a pool or hot tub water at a predetermined rate. Some dispense chlorine or bromine, while others dispense pH-adjusting chemicals.

Formed when chlorine and ammonia interact in pools due to sweat, biological substances, insects, and more, it can irritate skin and eyes.

A term used to describe any type of chlorine compound used as a disinfectant in a swimming pool and hot tub water or to kill, destroy or control bacteria and algae. In addition, chlorine oxidizes ammonia and nitrogen compounds caused by swimmers.

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

Circular pools, also known as round pools, are swimming pools built in a circle, producing a classic contemporary look.

Pool cleaners are several different chemicals, which, if used regularly as part of a maintenance program, ensure the pool and its equipment remain clean and sterile. Cleaning fluids include chlorines, algaecides, clarifiers, and stain removers.

Outdoor pools need to be closed during winter to protect the structure and equipment over the cold months. This process is also known as winterizing the pool.

Panel to operate aspects of the pool, provides easy, convenient control over water temperature, lighting, water features, automatic pool cover, and the moving floor if one has been fitted to the pool.

A mixture of wood and plastic forms an ultra-durable building material that resembles natural wood.

Also known as a stabilizer, pool conditioner protects chlorine from loss due to the sun’s UV rays (see Cyanuric Acid)

The cap or top lip on the pool or hot tub wall provides a finished edge around the pool or spa. It can be formed, cast in place or precast, or prefabricated with 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.

The etching, pitting, or eating away of the pool or hot tub or equipment. It can be caused by improper water balance, misuse of acid or acidic products, or soft water.

When placed on the water’s surface of a pool, hot tub, or hot tub, a cover increases the water temperature by absorbing and transmitting solar radiation, reducing evaporation, and preventing windborne debris from entering the water.

Allows bathers to use the pool for exercise by providing a solid current to swim against. Particularly suited to smaller pools.

Also known as a pool conditioner or stabilizer, cyanuric acid protects your pool’s chlorine from degradation due to sunlight.


Diatomaceous Earth — a porous substance used in certain types of pool filters.

The area surrounding a pool, typically concrete, wood, composite or natural stone.

A heated pool creates a lot of moisture in the air in the room it is in. This can lead to mold and dampness in your pool facilities. Dehumidifiers are vital in reducing air moisture and protecting your pool.

Comprehensive design and construction of a swimming pool to an agreed specification, working with a pool specialist.

A plumbing fitting is used to change the direction or redirect the flow of water. For example, some diverter valves are used on pool/spa combinations to allow the hot tub and then switch the flow back to the pool.

This term usually refers to a plumbing fitting installed on the suction side of the pump in pools, spas, and hot tubs. Sometimes called the main drain, it is located in the deepest part of the pool, hot tub or hot tub. It does not function as a drain on a kitchen sink. Pool main drains do not allow the water to drain to waste but rather connect to the pump for circulation and filtration.


Electric pool heaters heat the pool water in the form of electric resistance heaters or solar heaters. They are usually better suited to smaller home pools.

The design and blueprint for all the electrics that operate the pool, produced by the pool designer.

The process of digging a hole in the backyard is suitable for pool installation.

Exercise pools are small, also known as swim spas, typically built with jets to add resistance.

To ensure safety, pools are best designed and built by qualified professionals who are experts in their craft and have proven experience. The same applies to servicing the pool. In addition, experts will maintain the pool and ensure it gives many years of use.


Finespun filaments of glass are available in a rope or mat form. When used in polyester resins, catalysts and hardeners can be formed or molded into pools and spas.

A pool shaped like a figure 8

A device removes dissolved or suspended particles from water by recirculating the water through a porous substance (a filter medium or element). The three filters used in pools and spas are sand, cartridge, and D.E. (diatomaceous earth).

The rate at which the water is traveling through the filter, expressed in U.S. gallons per minute (GPM) per square foot of filter area.

The interior pool finish comprises the pool’s hard shell and the tiles or finishes that the water interacts with directly. The type of interior finish installed has an impact on the color and hue of the pool water.

The outside pool finish includes the tiling surrounding the pool and the walls and ceiling of the pool hall.

Additional swimming pool features include fire pits, fireplaces, fire bowls, and other enhancements that use fire.

Pool fittings include the drains and other plumbing parts used to pump water around your pool.

A flat, hard natural stone used for patios, walkways, decking, coping, and more.

A chemical that clumps floating particles in cloudy water, causing them to sink to the bottom, removed manually via vacuum

The quantity of water flowing past a designated point within a specified time, gallonage flowing past a point in 1 minute – also known as gallons per minute or GPM.

The part of an above-ground pool that secures the wall in place and provides much of the strength for the pool; generally made of coated steel, extruded aluminum, or resin.

Measures the amount of chlorine in a pool undisturbed by contaminants; contaminated chlorine is known as “combined chlorine.”

Freeform pools do not follow a specific shape, rather are characterized by their free-flowing curves.


Geometric pools are characterized by clean lines and sharp angles.

Glass pool tile is specially designed to withstand temperature changes, chemical damage, and submerged in water; glass pool tiles are often transparent or opaque.

Glossy pool tile is water-, chemical- and frost-resistant tile with a shiny exterior.

Abbreviation for “gallons per minute.”

Grecian pools typically have diagonal corners rather than sharply squared corners like those found in rectangle pools.

A grotto is a swimming pool water feature made of large rocks built above and around a large swimming area.

A paste-like mixture is applied between tiles that dry solid, creating an insoluble surface.

A mixture of cement and sand was sprayed onto contoured and supported surfaces to build a pool. Gunite is mixed and pumped to the site dry, and water is added at the point of application. Plaster is usually applied over the gunite.

There is an overflow trough at the edge of the pool through which floating debris, oil, and other “lighter-than-water” things flow. Pools with gutters usually do not have skimmers.


A screen attached to a frame attached to a telescopic pole is used to remove large floating debris, such as leaves and bugs, from the water’s surface.

Hardscapes refer to any hard landscaping building material, for example, concrete and natural stone.

A device located inside the heater provides heat transfer from the heat source to the water. This is usually a series of metallic tubes with fins located just above the flames.

A fossil-fueled, electric or solar device is used to heat a pool’s water, hot tub, or hot tub.

Hydrotherapy involves a low-intensity exercise in a pool to relieve the symptoms of range conditions, including arthritis.


An infinity pool creates the illusion of endlessness with a negative edge that spills over.

Inground pools are permanent pool structures built into the ground, usually in a back garden.

The pool pump pushes filtered water back into the pool through inlets, also known as jets.

The Institute of Swimming Pool Engineers is an organization that represents individual pool engineers. It covers a breadth of services, including promoting professional pool design, installing and maintaining pools and pool equipment, and engaging in the education and training of pool engineers. Learn more here.


Water jets feature in many pools, but particularly in hydrotherapy pools and spas. The powerful jets are used to relieve muscle tension and for relaxation.


Kidney pools are characterized by their unique shape that resembles a bean.


This refers to pools where the water level is exactly level with that of the pool surrounding.

Pool lighting, be it in-water or out, is used to create depth and aesthetics in a pool.

Also called a vinyl liner. The vinyl membrane acts as the container to hold or contain the water in some pools.

Liquid solar pool covers cover your pool with a thin film that protects water from evaporating.

L-shaped pools are created with two rectangular pools that form a 90-degree angle.


A plumbing fitting was installed on the suction side of the pump in pools, spas, and hot tubs. Sometimes simply referred to as the drain, it is located in the deepest part of the pool, hot tub, or hot tub. It does not function like the drain on a kitchen sink. Pool main drains do not allow the water to drain to waste but rather connect to the pump for circulation and filtration.

Pool maintenance is vital to keeping a pool clean and pleasant to use for a long time. It includes cleaning and managing the chemical balance of the pool water, among other things.

Mosaic pool tile is made of smaller pieces of tile that combine to create a larger design.

Moving floors are built into swimming pools to enable the owners to adjust the pool water depth, for example, shallower for young swimmers. One of the biggest attractions of a moving floor is the ability to raise its level with the external base and seal off the pool water completely. People can then stand on the solid base, and the area can be used for other functions such as parties.


A natural pool earns its name from its organic shape, materials, and colors. Natural pools also may be self-cleaning and operating.

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


This refers to the pool engineer re-opening an outdoor swimming pool after it has been closed for the winter (see the closing). The pool and plant room are cleaned, and the pool water chemistry is checked and adjusted as necessary.

Oval-shaped swimming pool.

A non-chlorine shocking compound that removes or destroys built-up contaminants and chloramines in pool water without raising chlorine levels.

An ozone sanitation system helps keep the pool water crystal clear and clean. It works by sanitizing the water and increasing the overall effectiveness of the filtration system.


A palapa is an open-air structure with a thatched roof, popular for its breezy design.

Pavers are small paving stones made of clay, brick, natural stone, or concrete.

A pergola is an open-air outdoor structure with four support beams and a lattice or crossbeam roof.

Abbreviation for Potential Hydrogen. Indicates the level of acidity or alkalinity of water on a scale ranging from 0-15. A low pH level can cause etched plaster, metal corrosion, and eye irritation. On the other hand, high pH can cause scale formation, chlorine inefficiency, and eye irritation. The ideal range for pH in swimming pools is typically 7.4 to 7.6.

A cover used on pools, spas, and hot tubs rest on the lip (coping) of the pool or hot tub deck, not a flotation cover. Used as a barrier to swimmers and bathers and for maintenance and thermal protection.

A term used to describe the pool’s area is located, be it a public or private pool.

To make outdoor pools really stand out, many pool owners decide to invest in hardscaping and landscaping. The right landscaping design can really make a pool something special.

The porcelain pool tile is a highly durable, richly colored product resistant to water and chemical and frost damage.

Parts per million

A mechanical device, usually powered by an electric motor, causes hydraulic flow and pressure to filtration, heating, and circulation of pool and hot tub water. Typically, a centrifugal pump is used for pools, spas, and hot tubs.

The volume of liquid a pump is capable of moving during a specified period. This is usually listed in gallons per minute or GPM.

Also called a pump performance curve. A graph that represents a pump’s water flow capacity at any given resistance.

Used as an alternative to chemical treatments to sanitize the pool.


The pool’s bond beam rises vertically in one part of the pool, creating a wall.

Pool shaped like a rectangle with clean lines and sharp corners.

A retaining wall protects your backyard from erosion and landslides caused by hills and inclines.

Roman-style swimming pools are recognizable for their rectangular shape bookended by two half-circles.


Chemical compounds are designed to kill bacteria, algae, and other living organisms. Also protects water from the effects of the sun.

A buildup of calcium that forms a white-grey powdery stain on pools.

The 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 caused by swimmers, the environment, and/or weather.

A device installed through the wall of a pool or hot tub connected to the pump’s suction line draws water and floating debris in the water flow from the surface without causing much flow restriction.

A removable, slotted basket or strainer placed in the skimmer on the suction side of the pump is designed to trap floating debris in the water flow from the surface without causing flow restriction.

When placed on the water’s surface of a pool, hot tub, or hot tub, a cover increases the water temperature by absorbing and transmitting solar radiation, reducing evaporation, and preventing windborne debris from entering the water.

A small, heated tub, often with built-in jets, designed for hydrotherapy and relaxation.

With the combination of “small” and “pool,” a spool is a small pool.

Stone veneer is a manufactured stone that simulates the look of natural stone and is applied to the exterior of outdoor structures, walls, and buildings.

A built-in swimming pool feature includes a sizeable horizontal shelf above the water for beverages and snacks and underwater bar stools.


See “Baja Shelf”

An apparatus or device used to monitor specific chemical residuals, levels, constituents, or demands in pool or hot tub water. The most common pool and hot tub water tests are pHs, total alkalinity, free available chlorine, water hardness, cyanuric acid, iron, and copper.

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

Usually made of resin or another form of plastic, the top cap covers the top plate and helps to give an above-ground pool a more finished, attractive look.

A top plate is attached to the top of each upright of an above-ground pool, providing connection points for the top track and top rails that span between each post.

Top rails form the top ledge of the swimming pool. Ranging up to 12″ in width, the rails connect between each post.

Sometimes called a stabilizer bar, the top track rests over the top of the wall but beneath the top rails. The top track interlocks from the top plate to the top plate helps to keep the top of the wall straight and help to keep the pool liner securely in place.

Measurement of the number of alkaline substances in your pool water.

Measures the number of minerals, chemicals, and other substances dissolved in your pool water

The cloudy condition of the water is due to the presence of microscopic 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.


The uprights or posts provide support for the wall and top frame of the pool. Uprights can range up to 12″ wide depending on the pool model and the material they are made of.


Devices that use suction to collect dirt from the bottom and sides of a pool or spa. Most common is a vacuum head with wheels that attaches to a telepole and is connected to the suction line, usually via the opening in the skimmer. Pool vacuums must be operated by a person, and debris is collected in the filter.

See “Infinity Pool”

The vinyl membrane acts as the container to hold or contain pool water.


The part of an above-ground pool that houses the water, typically made of galvanized steel.

Also called coagulant or flocculant. A chemical compound is used to gather (coagulate or agglomerate) or to precipitate suspended particles so they may be removed by vacuuming or filtration. There are two types; inorganic salts of aluminum (alum) and other metals or water-soluble organic polyelectrolytes.

Additional swimming pool features include waterfalls, water bowls, fountains, bubblers, deck jets, and other elements that incorporate water.

Tile that is installed at the pool’s waterline, right below the coping and decking. Waterline tile must be highly durable water-resistant since it is constantly submerged in pool water.

The small floating “door” on the side of the skimmer faces the water over which water flows to the skimmer. Adjusts automatically to small changes in water level to assure a continuous flow of water to the skimmer. The weir also prevents debris from floating back into the pool after the pump shuts off. Also known as a skimmer weir.


The edges of a zero-edge pool spill over, creating an illusion of boundlessness.

Also known as a “beach entry pool,” these pools have a slightly sloped entry that resembles a beach.

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