back-flow - Flow of water in a pipe or line in a direction opposite to normal flow. Often associated with back siphonage or the flow of possibly contaminated water into a potable water system.
back-flow preventer - A device or system installed in a water line to stop back-flow. (See vacuum breaker, air gap.)
backwash - The process in which beds of filter or ion exchange media are subjected to flow opposite to the service flow direction to loosen the bed and to flush suspended matter collected during the service run.
bacteria - Unicellular prokaryotic microorganisms which typically reproduce by cell division.
bed - The ion exchanger or filter media in a column or other tank or operational vessel.
bed depth - The height of the ion exchanger or filter media in the vessel after preparation for service.
bed expansion - The increase in the volume of a bed of ion exchange or filter media during upflow operations, such as backwashing, caused by lifting and separation of the media. Usually expressed as the percent of increase of bed depth.
bicarbonate alkalinity - The alkalinity of a water due to the presence of bicarbonate ions (HCO3).
biodegradable - Subject to degradation to simpler substances by biological action, such as the bacterial breakdown of detergents, sewage wastes and other organic matter.
bleach - An oxidizing agent formulated to break down colored matter. Includes the widely used hypochlorites, as well as perborates and other special purpose materials.
brackish water - Water having salinity values ranging from approximately 500 to 5,000 parts per million (milligrams per liter).
breakpoint chlorination - A chlorination procedure in which chlorine is added until the chlorine demand is satisfied and a dip (breakpoint) in the chlorine residual occurs. Further additions of chlorine produce a chlorine residual proportional to the amount added.
brine - A strong solution of salt(s), such as sodium chloride used in the regeneration of ion exchange water softeners, but also applied to the mixed sodium, calcium and magnesium chloride waste solution from regeneration.
builder - A chemical incorporated in a detergent formulation to produce a desired alkalinity level and improve the ability to suspend soil. The alkaline phosphates are widely used for this purpose.
bypass - A connection or a valve system that allows untreated water to flow through a water system while a water treatment unit is being regenerated, backwashed or serviced; also applied to a special water line installed to provide untreated water to a particular tap, such as a sill cock.
