Learn about the different types of contaminants that might put your family at risk.

The removal of excess chlorine residual, often after super-chlorination.  (See super-chlorination.)
The removal of all ionized minerals and salts (both organic and inorganic) from a solution by a two phase ion exchange procedure.  First, positively charged ions are removed by a cation exchange resin in exchange for a chemically equivalent amount of hydrogen icons.  Second, negatively charged ions are removed by an anion exchange resin for a chemically equivalent amount of hydroxide ions.  The hydrogen and hydroxide ions introduced in this process unite to form water molecules.  The term is often used interchangeably with demineralization. 
The removal of ionized inorganic minerals and salts (not organic materials) from a solution by a two-phase ion exchange procedure; similar to deionization, and the two terms are often used interchangeably. 
The mass of a substance per specified unit of volume; for example, pounds per cubic foot.  True density is the mass per unit volume excluding pores; apparent density is the mass per unit volume including pores.
diaphragm pump
A form of positive displacement pump in which the reciprocating piston is separated from the solution by a flexible diaphragm, thus protecting the piston from corrosion and erosion and avoiding problems with packing and seals. 
diatomaceous earth, diatomite
A processed, natural material, chiefly the skeletons of diatoms, used as a filter medium. 
differential pressure
The difference in pressures at two points in a water system; may be due to differences in elevation or to friction losses or pressure drops due to resistance to flow in pipes, softeners, filters or other devices.
The process whereby particles of liquids intermingle as the result of their spontaneous movement in dissolved substances moving from a region of high concentrations to one of low concentration.
A process in which pathogenic (disease producing) bacteria are killed; may involve disinfecting agents such as chlorine or physical processes such as heating.
The separation of molecules into positively and negatively charged ions in water solution.
dissolved solids
The weight of matter in true solution in a stated volume of water; includes both inorganic and organic matter; usually determined by weighing the residue after evaporation of the water at 105 or 180° C. 
(See collector.)
A specific form of limestone (CaMg (CO3)) 2 containing chemically equivalent concentrations of calcium and magnesium carbonates; the term is sometimes applied to limestone with compositions similar to true dolomite.
A slang term sometimes applied to water conditioning equipment designed for residential use.
A term applied to designate the direction (down) in which water or a regenerant flows through an ion exchanger or filter during any phase of the operating cycle.  Also referred to as co-current flow.
Active, alive, or tending to produce motion as opposed to static, resting, or fixed. 
dynamic system
A system or process in which motion occurs, or includes active forces, as opposed to static conditions with no motion.