Glossary of Terms - D
A B C D E F G H I J K L M N O P Q R S T U V W Z
dechlorination - The deliberate removal of chlorine residual.
deionization - The removal of all ionized minerals and salts from a solution by a two-phase ion exchange process. First, positively charged ions are removed by a cation exchange resin in exchange for a chemically equivalent amount of hydrogen ions. 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, commonly abbreviated as DI, is often used interchangeably with demineralization. (See demineralization, ion exchange.)
demineralization - The removal of ionized minerals and salts from a solution by a two-phase ion exchange procedure, similar to deionization, and the two terms are often used interchangeably. (See deionization, ion exchange.)
density - 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. (See specific gravity.)
depth filtration - A filtration process in which water flows through progressively smaller pore spaces in a filter media bed.
detergent - Any material with cleansing powers, including soaps, synthetic detergents, many alkaline materials and solvents, and abrasives. In popular usage the term is often used to mean the synthetic detergents.
D.I. or DI - Abbreviation for "deionization".
dialysis - The separation of components of a solution by diffusion through a semi-permeable membrane which is capable of passing certain ions or molecules while rejecting others. (See electrodialysis)
diaphragm pump - A 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 related problems with packing and seals.
diatomaceous earth - A fine, siliceous (made of silica) “earth” composed mainly of the skeletal remains of diatoms, a type of free-floating, microscopic plant found in the ocean. Diatomaceous earth is used as a water filtration medium.
diatomite - Another name for diatomaceous earth.
dielectric fitting - A plumbing fitting made of, or containing, an electrical nonconductor, such as plastic; used to separate dissimilar metals in a plumbing system to control galvanic corrosion.
differential pressure - See pressure differential.
digestion - The process in which complex materials are broken down into simpler substances; may be due to chemical, biological or a combination of reactions. (See sterilization.)
disinfection - A treatment of water to inactivate, destroy, and/or remove pathogenic (disease producing) bacteria, viruses, cysts, and other microorganisms (but not completely eliminating all microorganisms) for the purpose of making the water microbiologically safe for human consumption. It may use chlorine, iodine, ozone, or hydrogen peroxide; or it may involve physical processes such as distillation, micro-filtration, ultra-filtration, boiling, or ultraviolet radiation.
dissociation - The separation of molecules into positively and negatively charged ions; occurs when salts dissolve in water. (See ionization.)
dissolved solids - The weight of matter, including both inorganic and organic matter, in true solution in a stated volume of water.
distillation - The process in which a liquid, such as water, is converted into its vapor state by heating, and the vapor cooled and condensed to the liquid state and collected; used to remove solids and other impurities from water; multiple distillations are required for extreme purity.
distributor - A device or system designed to produce even flow through all sections of an ion exchanger or filter bed, and to retain the media in the tank or vessel; usually installed at the top and bottom of loose media systems. (See collector.)
dolomite [CaMg(CO3)2] - A carbonate mineral of calcium and magnesium found in nature in extensive beds of compact limestone and marble that are rich in magnesium carbonates.
down-flow - A term designating the direction (down) in which water or a regenerant flows through an ion exchanger or filter during any phase of the operating cycle.
drain - A pipe or conduit in a building plumbing system which carries liquids to waste by gravity; sometimes the term is limited to liquids other than sewage.
drain line - A tube or pipe from a water conditioning unit that carries backwash water, regeneration wastes and/or rinse water to a drain or waste system.
driven well - A shallow, usually small well (having a diameter of 1.5 inches to 3 inches or 4 to 10 cm) constructed without the aid of any drilling, boring, or jetting device, by driving a series of connected pipe lengths into unconsolidated material to a water-bearing stratum.
dug well - A shallow, large diameter well constructed by excavating with power machinery or hand tools instead of drilling or driving. Typically a dug well is constructed for an individual residential water supply and yields considerably less than 100 US gallons per minute.