Cross-Connection. In plumbing, a physical connection through which a supply of
potable water could be contaminated, polluted, or infected. A physical connection
between water supplies from different systems.
Dam. A barrier constructed across a watercourse for the purpose of (1) creating a
reservoir, (2) diverting water from the reservoir into a conduit or channel, (3) creating a
head which can be used to generate power, and (4) improving river navigability.
Dechlorination. The partial or complete reduction of residual chlorine in a liquid by any
chemical or physical process.
Demanganization. In water treatment, the removal of compounds of manganese from
Demineralization. Reduction of the mineral content of water by a physical or chemical
process; removal of salts.
Deoxygenation. Depletion of the dissolved oxygen content in a liquid.
Detention Time. The theoretical length of time for water to pass through a basin or
tank, of all the water moves through with the same uniform velocity; mathematically
equal to the volume of basin divided by the rate of flow.
Diffuser. A porous plate, tube, or other device through which air is forced and divided
into minute bubbles for diffusion in liquids. Commonly made of Carborundum,
Alundum, metal, or plastic materials.
Discharge. (1) As applied to a stream, the rate of flow or volume of water flowing at a
given place within a period of time. (2) The process of water or other liquid passing
through an opening or along a conduit or channel. (3) The water or other liquid which
emerges from an opening or passes along a conduit or channel.
Disinfectant. Any oxidant, including but not limited to chlorine, chlorine dioxide,
chloramines, and ozone added to water in any part of the treatment or distribution
processes, that is intended to kill or inactivate pathogenic microorganisms.
Disinfection. The process of killing or inactivating most (but not necessarily all) of the
harmful and objectionable microorganisms in a fluid by various agents such as
chemicals, heat, ultraviolet light, ultrasonic waves, radiation, etc.
Dissociation. The dissolving of molecules of a substance in water into positive and
negative ions. Also called ionization.
Dissolved Solids. Solids that are present in solution.