Distillation. The process of converting a liquid to a gaseous or vaporous state and
condensing the resulting vapor to liquid under the influence of heat (and possibly
reduced pressure or partial vacuum), followed by cooling. Used to remove impurities
from a liquid in order to improve its purity.
Dose Equivalent. The product of the absorbed dose form ionizing radiation and such
and its distribution in the body as specified by the International Commission on
Drawdown. The lowering of the water surface in a well, and of the water table or
piezometric surface adjacent to the well, resulting from the withdrawal of water from the
well by pumping. Drawdown is the difference between static level and pumping level.
Dry Feeder. A feeder for dispensing a chemical or other fine material in the solid state
to water or wastewater at a rate controlled manually or automatically by the rate of flow.
The constant rate may be either volumetric or gravimeteric.
E. Coli. See Escherichia coli.
Effective Size. The size of sieve which will permit 10 percent (by weight) of the sand
sample to pass but will retain the remaining 90 percent. A measure of the relative
ability of a filtering material to permit the passage of water.
Effluent. (1) A liquid which flows out of a containing space. (2) Water, or other liquid,
partially or completely treated or in its natural state, which flows out of a reservoir,
basin, treatment plant, or part thereof.
Electrolysis. Chemical changes in an electrolyte caused by an electrical current. The
use of this term to mean corrosion by stray currents should be discouraged.
Element. A substance which cannot be subdivided into simpler substances by ordinary
Elevated Storage. In any distribution system, storage of water in a tank supported on a
Escherichia Coli (E. Coli). One of the species of bacteria in the coliform group. Its
Eutrophic Lake. Lake or other contained water body rich in nutrients. Characterized by
a large quantity of planktonic algae, low water transparency with high dissolved oxygen
in upper layer, zero dissolved oxygen in deep layers during summer months, and
brown- or black-colored organic deposits.