Glossary of Water Treatment Terms & Definitions - P



A term used to describe visible sediment particles, used as both singular and plural.

Parts Per Billion (ppb)

A basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of a dissolved or suspended constituent, per billion parts by weight of water or other solvent. One part per billion is equal to one microgram per liter, the preferred unit.

Parts Per Million (ppm)

A common basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of water or other solvent. In dilute water solutions, one part per million is practically equal to one milligram per liter, which is the preferred unit. 17.l ppm equals one grain per US gallon. One ppm equals one pound per million pounds of water.

pH (potential of Hydrogen)

An expression of the acidity of a solution; the negative logarithm of the hydrogen ion concentration (pH 1 very acidic; pH 14, very basic; pH 7, neutral). e.g., pH 5 is 10 times the acidity of 6 and 100 times the acidity of 7. pH is a measure of intensity and not capacity. It is the logarithm of the reciprocal of the hydrogen ion concentration of a solution. The neutral point of 7 indicates the presence of equal concentrations of free hydrogen and free hydroxide ions.

Pharmaceutical Grade Water

The definition of six grades of water by the U.S. Pharmacopoeia is as follows: 1.) Purified water 2.) Water for injection 3.) Bacteriostatic water for injection 4.) Sterile water for inhalation 5.) Sterile water for injection 6.) Sterile water for irrigation.


An acid-base indicator which produces no color in an acid solution but turns pink or red in an alkaline solution.

Physical Adsorption (Van der Waals Adsorption)

Binding of adsorbate to the surface of a solid by forces whose energy levels approximate those of condensation.

Physical Stability

The quality which an ion exchange resin must possess to resist changes that might be caused by attrition, high temperatures, and other physical conditions.

Point of Entry (POE)

A water treatment device which installs at the main inlet to a building and acts as centralized treatment.

Point-of-Use (POU)

A water treatment system designed to connect at the actual point-of-use for water; countertop or undersink treatment systems.


A sequestering agent used to tie up hardness and iron in solution. As a coating agent, it forms a thin passivating film on metal surfaces to control corrosion.


The complex network of channels in the interior of a particle of a sorbent.

Portable Exchange

Water softeners, deionizers, and filters which are designed for removal from its point of application for transport to a central station or plant for regeneration or servicing.

Positive Charge

The electrical potential acquired by an atom which has lost one or more electrons; a characteristic of a cation.

Potable Water

Water which is considered safe and fit for human consumption, culinary and domestic purposes and meets the requirements of the health authority having jurisdiction.

Powdered Activated Carbon

Activated carbon in particle sizes predominantly smaller than 80 mesh.


The abbreviation for "parts per billion".


The abbreviation for "parts per million".


The application of chlorine to a water prior to other water treatment processes.


To cause a dissolved substance to form a solid particle that can be removed by settling or filtering. The term also refers to the solid thus formed.

Preferential Adsorption

Adsorption in which a certain component or certain components are adsorbed to a much greater extent than others.

Pressure Drop

A decrease in water pressure during its flow due to internal friction between molecules of water, and external friction due to irregularities or roughness in surfaces past which the water flows.


Any of a large group of mostly microscopic, one celled animals living chiefly in water. Many protozoa's are parasitic and are higher on the food chain than the bacteria they eat.


A natural, glassy aluminum silicate mineral from volcanic ash which is used as a water treatment filtration media.


The removal of undesirable matter from water or wastewater. It is the disinfection of water by the killing of microbial contaminants, such as coliform bacteria. A strict definition means the removal from water of all contaminants.


Biological decomposition of organic matter by microbes with the production of ill smelling products. Usually takes place when there is a deficiency of oxygen.


Substances which produce fever when introduced into humans. Being chemically stable, pyrogens are not necessarily destroyed by conditions that kill bacteria. Pyrogenic means to cause heat.


A super oxidation media serving as a catalyst in the removal of iron, hydrogen sulfide and manganese. It works best at or above a pH of 6.5 and requires no regeneration. Adequate backwashing is necessary to provide at least 20 per cent bed expansion of this 120 lb. per cubic foot media.



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