Swimming Pool Terms Glossary



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Part Per Million Abbreviated as ppm. It is a "weight-to-weight" expression. It means one part in one million parts, such as, 1 pound of chlorine in one million pounds of water or 119,904 gallons. Many of the common pool water tests as well as acceptable ranges are stated as ppm. For instance, Free Available Chlorine should be kept between 1.0 and 3.0 ppm; Total Alkalinity should be between 80 and 120 ppm; and Water Hardness should be between 200 and 400 ppm. A ppm and a milligram per liter (mg/L) are considered equal.

Perimeter The distance around the outer edge of a shape.

Peroxide Any compound containing the two oxygen atoms united together into a bivalent– O-O group. Readily releases abnormally active atomic oxygen, and therefore any peroxide is a strong oxidizer. Examples are hydrogen peroxide and potassium peroxymonosulfate

Pesticide Any chemical or compound that kills insects, weeds, rodents, or any other thing considered a pest. In pools that is bacteria, virus, algae and the like. All pesticides must be registered by the U.S. EPA.

Petcock A small, manually-operated faucet or valve for draining off liquids or releasing air pressure. The air-relief valve on a filter is an example.

pH A term used to indicate the level of acidity or alkalinity of pool water. Too low pH causes etched plaster, metal corrosion and eye irritation. Too high pH causes scale formation, poor chlorine efficiency and eye irritation. Proper range for pH in swimming pools is 7.4 to 7.6. It is always written with a lower case "p" and a capital "H."

pH Decreaser A chemical that decreases or lowers the pH of the water. Muriatic acid, dry acid and sodium bisulfate are examples.

pH Increaser A chemical that increases the pH of the water. Soda ash, sodium sesquicarbonate and sodium bicarbonate are examples of pH increasers.

Phenol Red A chemical reagent dye used to test for pH. It can measure pH from 6.8 to 8.4.

Phosphate An essential growth constituent of organisms and can be a nutrient that limits the primary productivity of a body of water. Excess phosphates or phosphorus in water can cause excessive algal growth stimulation to sometimes nuisance quantities. Phosphate in water is measured as phosphate ion.

Plaster A mixture of white cement and white marble dust used as an interior finish which can be tinted, colored or left white, applied to the gunite or shotcrete of a pool or spa.

Pollutant Any contaminant high enough to endanger the aquatic environment or the public health.

Polymer A 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 is called polyethylene.

Poly Vinyl Chloride (PVC) An artificial polymer made from vinyl chloride monomer and frequently used in pipes, sheets and vessels for transport, containment, water treatment facilities, pools and spas.

Potassium Peroxymonosulfate Active ingredient and chemical name of a non-chlorine shock treatment or non-chlorine oxidizer. Does not kill bacteria or algae but it will oxidize or destroy ammonia, nitrogen and swimmer waste. It has a low pH and it does not increase chlorine or bromine levels the way that superchlorination does, so water may be entered in 15 minutes after addition. Also, it will reactivate bromine to its killing form, hypobromous acid.

ppm Abbreviation for parts per million. It is a weight to weight expression. It means one part in one million parts, such as, 1 pound of chlorine in one million pounds of water or 119,904 gallons. Many of the common pool water tests as well as acceptable ranges are stated as ppm. For instance, Free Available Chlorine should be kept between 1.0 and 3.0 ppm; Total Alkalinity should be between 80 and 120 ppm; and Water Hardness should be between 200 and 400 ppm.

Precipitate A substance separating, in solid particles, from a liquid as a result of a chemical or physical change. It also means to form a precipitate.

Precoat Refers to the depositing of diatomaceous earth (D.E.) onto the filter grids or elements. A very fine granular filter medium, such as D.E., applied (usually by slurry) to a retaining membrane or fabric surface prior to a service run.

Pre-dilute To dilute a chemical before adding it to the pool or spa water.

Pressure The force pushing on a unit area. Water pressure is normally measured in pounds per square inch (psi) or feet of head.

Pressure Gauge A gauge with an analog dial indicating the pounds per square inch (PSI) of pressure that has built up within a closed container such as a filter.

Prime To fill a pump casing or siphon with water to remove air. Most pumps must be primed before start-up or they will not pump water.

PSI An abbreviation for pounds per square inch.

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 is used for pools, spas and hot tubs.

Pump Capacity The volume of liquid a pump is capable of moving during a specified period of time. This is usually gallons per minute (gpm).

Pump Curve – also called a pump performance curve – A graph that represents a pump's water flow capacity at any given resistance.

Pump Strainer Basket A device placed on the suction side of the pump, which contains a removable strainer basket designed to trap debris in the waterflow without causing much flow restriction. Sometimes called a "hair and lint trap."

PVC Abbreviation for Poly Vinyl Chloride. An artificial polymer made from vinyl chloride monomer and frequently used in pipes, sheets and vessels for transport, containment, water treatment facilities, pools and spas.

PVC Pipe A type of pressure pipe for water distribution manufactured from poly vinyl chloride compound. Many pools and spas are plumbed with this type of pipe.



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