A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

PARTICLE SIZE - As used in industry standards, the size of a particle suspended in water as determined by its smallest dimension, usually expressed in microns.

PARTS PER MILLION (PPM) - A common basis for reporting the results of water and wastewater analysis, indicating the number of parts by weight of a dissolved or suspended constituent, per million 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.

PATHOGEN - An organism which may cause disease.

pH - stands for "potenz hydrogen"., German for "potential of hydrogen". In water chemistry, pH is expressed as the concentraton of hydrogen ions to hydroxl ions. The pH scale is a logrithmic scale from 1 to 14, with 7 being neutral; above 7, more alkaline; and below 7 more acidic.

PPM - The abbreviation for "part per million".

PRECIPITATE - To cause a dissolved substance to form a solid particle which can be removed by settling or filtering, such as in the removal of dissolved iron by oxidation, precipitation, and filtration. The term is also used to refer to the solid formed, and to the condensation of water in the atmosphere to form rain or snow.

RATED CAPACITY - The basis for calculating the period of time, or number of gallons delivered by a water softener or filter, between regenerations or servicing, as determined under specific test conditions.

RATED SERVICE FLOW - The manufacturer's specified maximum flow rate at which a water softener will deliver soft water or a filter will deliver quality water as specified for its type, as determined under standard test conditions. A manufacturer may also specify a minimum flow rate or a range of service flows.

RAW WATER - Untreated water, or any water before it reaches a specific water treatment device or process.

RED WATER - Water which has a reddish or brownish appearance due to the presence of precipitated iron and/ or iron bacteria.

REGENERANT - A solution of a chemical compound used to restore the capacity of an ion exchange system. Sodium chloride brine is used as a regenerant for ion exchange water softeners, and acids and bases are used as regenerants for the cation and anion resins used in demineralization.

RESIDUAL - The amount of a specific material remaining in the water following a water treatment process. May refer to material remaining as a result of incomplete removal (see leakage) or to material meant to remain in the treated water (see residual chlorine).

RESIN - Synthetic organic ion exchange material, such as the high capacity cation exchange resin widely used in water softeners.

REVERSE OSMOSIS - A process for the removal of dissolved ions from water in which pressure is used to force the water through a semipermeable membrane which will transmit the water but reject most other dissolved materials.