Pool Terminology

Whether you are considering building a new pool, you are in the process of a build or you are a pool owner, this page of key industry terms will help you better understand some of the language that is spoken in the pool world!

  • Acid: A liquid or dry chemical used to lower the pH and/or alkalinity of pool or spa water.
  • Acid Wash: A procedure using an acid solution to clean an interior surface of a pool with subsequent neutralization of the acid.
  • Aggregate: Marble dust, sand, rocks, pebbles, colored quartz, dolomite and other similar materials used as components of concrete or plaster.
  • Air Blower: A device that produces a continuous flow of air.  
  • Algae: Minute plant life growing in water in the presence of sunlight and carbon dioxide.
  • Anti-vortex Drain Cover: A plate or cover that is affixed to the main outlet of a swimming pool or spa that prevents a vortex from forming as water passes through to the main outlet.
  • Backfilling: Filling space between pool shell and sides of excavation with dirt.
  • Back Pressure: Resistance to flow, normally expressed in pounds per square inch (kilograms per square centimeter)
  • Backwash: Process of running water through a filter opposite the normal direction of flow to flush out contaminants.
  • Balance: The term in water chemistry to indicate that when measuring all components together, the water is neither scaling nor corrosive.
  • Ball Valve: A device utilizing a ball-shaped diverter to partially or totally obstruct the flow of water.  
  • Barrier: A means to limit, delay, or restrict access to a pool, spa, or hot tub.
  • Bleeder Valve: A device that allows air to be vented from a system.
  • Blister: An area of raised surface detached from the structural matrix of a material.
  • Blower: An electromechanical device that generates air pressure to provide spa jets and rings with bubbles.  
  • Bond Beam: Reinforced masonry units designed to resist horizontal forces.
  • Bonding (electrical): The joining of metallic parts to form an electrically conductive path, which will ensure electrical continuity.
  • Booster Pump System: A pump that is completely independent of the filtration and heating system.  Used to provide support for hydrotherapy jets, cleaning systems and gas chlorinators or special water features.
  • Break in Grade: Occurs when the slope of the pool floor changes to a greater slope.
  • Brown Coat: A coat of plaster applied with a fairly rough texture to receive the finish coat.
  • BTU: British Thermal Unit. A unit of measurement used to define the capabilities of heaters.  One BTU is capable of raising the temperature of one pound of water by one degree Fahrenheit.  
  • Bull Nose: A brick or stone with a rounded corner.
  • Cantilever: A projecting beam supported only at one end.
  • Cartridge: Disposable element containing filtering media and used in some pool filters.
  • Cartridge Filter: A filter that utilizes a porous element that acts as a filter medium.
  • Cement: A powdered substance of lime and clay generally mixed with water and aggregate to make concrete.
  • Check Valve: A valve that permits flow of water or air in only one direction through a pipe.
  • Checks (surface): Spider webbing pattern in a surface.  Not all the way through, not an open crack.
  • Chlorine: A substance used to sanitize water by oxidizing (killing) bacteria; generally available in liquid, solid (tablets or sticks), and granular form.
  • Circuit Breaker: A device designed to open and close an electrical circuit manually, and to open a circuit automatically at a predetermined over current level, thus providing protection to the wiring and electrical components.
  • Circulation System: An arrangement of mechanical equipment and/or components designed to ensure even distribution of heat, chemicals, and filtration of water throughout the pool.  Includes filters, heaters, pumps, chlorinators, piping, inlets, drains, skimmers and other appurtenances. 
  • Coping: The cap on the wall that provides a finishing edge around the pool/spa. Can be formed, cast in place, precast, brick, stone, or pre-fabricated from metal or plastic material. 
  • Cove: The radius that joins the floor and wall of a pool/spa.
  • Crack (surface): A repairable break in the surface, no major, not self-curing.
  • Crack (structural): A break or split which weakens the structural integrity of the pool.
  • Craze: See checks.
  • Decks: Those areas immediately adjacent to or attached to a pool or spa that are specifically constructed or installed for sitting, standing, or walking.  Generally made of concrete, wood, or masonry.
  • Deep Area: Water depth areas exceeding five feet (5').
  • Diatomaceous Earth (DE): A white, powdery substance composed of tiny prehistoric skeletal remains of algae (diatoms), used as a water filtration media in DE filters. 
  • Diatomaceous Earth (DE) Filter: Pool filter using DE as filtering method.
  • Diverter: Plastic or bronze adapter pipe that fits into a skimmer port to facilitate connection of a vacuum hose.  The diverter can divert all suction to the skimmer, closing off the main drain or vice versa.
  • Erosion: 1. Act of destroying or dissolving by slow disintegration or wearing away.  2. In an erosion feeder, it is the way water dissolves the chemical being fed.  
  • Etching: Corrosion of a surface by water that is acidic or low in total alkalinity or hardness.
  • Evaporation: Conversion of liquid molecules into vapor.
  • Expansive Soil: Clay soils that absorb moisture and swells, creating the potential for damage to a structure.
  • Feet of Head: The resistance in a hydraulic system based on the equivalent to the height of a column of water that causes the same resistance (100 feet of head equals 43 pounds per square inch). The total dynamic head in the sum of all resistances in a complete operating system.
  • Filter: Device for removing suspended particles from pool water.
  • Filter Cycle: Time of filter operation between backwashes.
  • Filter Element: A device within a filter tank designed to entrap solids and conduct water to a manifold, collection header, pipe, or similar conduit and return it to the pool, spa, or hot tub.  A filter element usually consists of a septum and septum support or a cartridge.
  • Filter Media: Fine-grain materials in filter trap matter suspended in pool water.
  • Flow Rate: The volume of liquid flowing past a given point in a specified time period.  Usually expressed as U.S. gallons per minute (gpm) or gallons per hour (gph). 
  • Friction Head: Head specifically caused by friction or drag.
  • GPD: Gallons per day.
  • GPH: Gallons per hour.
  • GPM: Gallons per minute.
  • Hardness: Also called "calcium hardness". The amount of dissolved minerals (mostly calcium and magnesium) in a body of water. In unbalanced water, high levels cause scale and low levels corrode surfaces and equipment.
  • Heater: A fossil-fueled, electric or solar device to heat the water of a pool or spa.
    • Fossil-fueled heaters use natural, propane gas or fuel oil and utilize an open flame to heat a heat exchanger.
    • Electric heaters utilize a heating element immersed in water.
    • Solar heaters utilize ultraviolet rays of the sun to heat the water.

      Other ways to categorize heaters include:
    • Direct heaters that heat the tubes in which water circulates.
    • Indirect heaters that circulate steam or hot water inside a heat exchanger through which water flows.
  • Hydrotherapy Jet: A fitting that blends air and water creating a high-velocity turbulent stream of air-enriched water.
  • Impeller: The rotating vanes of a centrifugal pump; its action creates the flow of the water.
  • Influent: The water entering a filter or other device.
  • Jets: See Hydrotherapy Jets.
  • Manifold: A pipe with several openings for making multiple corrections.
  • Muriatic Acid: A dilute solution of hydrochloric acid used to lower alkalinity and clean masonry surfaces.
  • O-Ring: Thin rubber gasket used to create a waterproof seal in certain plumbing joints or between two parts of a device, such as between the lid and the strainer on a pump.
  • Overflow System: Refers to removal of pool/spa surface water through the use of overflows, surface skimmers, and surface water collection systems of various design and manufacture.
  • pH: Measure of acidity or alkalinity of water; pH of 7 is neutral, below 7 is acidic, and above 7 is alkaline.
  • PPM: Parts per million (in a pool, parts of a chemical or mineral per million parts of water, by weight).
  • Plaster: A type of interior finish (a mixture of white cement and aggregate , which will accept a tint of color) which is applied to a concrete pool or spa. Also called Mar-cite or Marblite.
  • PSI: An abbreviation for pounds per square inch.
  • Pumice: A natural soft, abrasive stone substance (similar to lave rock) used to clean pool tiles.
  • Pump: 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 and spa water.  Typically, a centrifugal pump design is used for pool and spas.
  • PVC: Polyvinyl chloride is thermoplastic resin commonly used for pool piping and plumbing components.
  • Reinforcing Bar (Rebar): Steel bars embedded in concrete to increase its ability to withstand bending and stretching.
  • Return Inlet: The aperture or fitting through which the water under positive pressure returns into a pool or spa.
  • Sand Filter: Pool filter using sand as filtering medium.
  • Scale: The precipitate that forms on surfaces in contact with water when the calcium hardness, or pH, or total alkalinity levels are too high.
  • Screed: In cement masonry flatwork, the wood or metal straightedge used to strike off or level newly placed concrete.
  • Shotcrete: A mixture of cement and sand, applied onto contoured and supported surfaces to build a pool or spa.  Shotcrete is premixed and pumped wet to the construction site.
  • Shocking: See Super-chlorination.
  • Skimmer: A part of the circulation system that removes debris from the surface of the water.
    Through-wall: A device installed in the wall of an inground pool or spa or aboveground/onground pool that permits the continuous removal of floating debris and surface water to the filter.
    Over-the-wall: A device installed over the wall of an aboveground/on-ground pool that allows for continuous removal of debris and surface water to the filter.
  • Slope: An inclined surface.
  • Strainer Basket: Device in skimmer and input side of pump used to catch large pieces of debris in pool water.
  • Suction Outlet: The aperture or fitting through which the water under negative pressure is drawn from the pool or spa.
  • Super-chlorination: Periodic application of extremely high levels of chlorine in (in excess of 3 ppm) to completely oxidize any organic material in a body of water and leave a substantial chlorine residual. Also called "shocking".
  • Swimming Load: Number of people using pool at a given time.
  • Test Kit: A device used to monitor specific chemical residual or demands in pool or spa water. 
  • Three-Port Valve: A plumbing fitting used to divert flow from one direction into two other directions. 
  • Time Clock: A mechanical device that automatically controls the periods that a pump, filter, heater, blower and other electrical devices are on.
  • Total Dynamic Head: See Feet of Head.
  • Turnover Rate: Number of times all the pool water passes through filter in a given time period.
  • Underwater Light: A fixture designed to illuminate from beneath the water surface.
    Wet niche light: A watertight and water cooled light unit placed in a submerged niche in a pool, spa, or hot tub wall and accessible only from the pool.
    Dry niche light: A light unit placed behind a watertight window in the pool, spa, or hot tub wall.
  • Valve: Any device in a pipe that will partially or totally obstruct the flow of water (such as with a ball, gate, or glove valve) or permit flow in one directin only (as with a check or foot valve).
    Bleeder valve: A device that allows air to be vented from a system.
    Multiport valve: A device that allows for the multi-directional control of the passage or flow of water through a system.                                                                                                                           Push-pull valve: A device that allows for the dual directional controls or flow of water through a system.
  • Venturi Jet: See Hydrotherapy Jets.
  • Vertical Wall: Shall refer to the wall up to a positive 11-degree angle towards the pool's interior from plumb.
  • Walls: The interior pool or spa wall consisting of surfaces from the plumb to a 45 -degree slope.
  • Waterline: The waterline shall be defined in one of the following ways:
    Skimmer System: The waterline shall be at the midpoint of the operating range of the skimmers when there are no users in the pool or spa.
    Overflow System: The waterline shall be at the top of the overflow rim.
  • Weir: The barrier in a skimmer over which water flows.  A floating weir raises and lowers its level to match the water level in a pool or spa.
  • Wet Niche: See Underwater Light.