Velocity, Mean. The average velocity of a stream flowing in a channel or conduit at a
given cross section or in a given reach. It is equal to the discharge divided by the
cross-sectional area of the section, or the average cross-sectional area of the reach.
Also called average velocity.
Venturi Meter. A meter for measuring the rate of flow of a liquid through closed
conduits or pipes, consisting of a venturi tube and one of several proprietary forms of
flow registering devices.
Virus. The smallest (10 to 300 millimicrons in diameter) form capable of producing
infection and disease in humans or other large species. The true viruses are
insensitive to antibiotics. They multiply only in living cells where they are assembled as
complex macromolecules utilizing the cells' biochemical systems. They do not multiply
by division as do intracellular bacteria.
Volatile. Passing off readily in the form of a vapor.
Volatile Synthetic Organic Chemicals (VOCs). A general class of organic chemicals
which are relatively volatile. The primary VOCs identified by the EPA as affecting
safety of drinking water are trichloroethylene, tetrachloroethylene, carbon tetrachloride,
trichlorethane, dichloroethane, methylene chloride, and vinyl chloride. These
chemicals in water supplies result from industrial contamination.
Water. A chemical compound consisting of two parts of hydrogen and one part of
oxygen by volume and usually having other solid, gaseous, or liquid materials in
solution or suspension.
Water-Bearing Formation. A term, more or less relative, used to designate a geological
formation that contains considerable groundwater. It is usually applied to formations
Watercourse. A channel in which a flow of water occurs, either continuously or
intermittently, and if the latter, with some degree of regularity. Such flow must be in a
definite direction. Watercourses may be either natural or artificial, and the former may
occur either on the surface or underground. A different set of legal principles may
apply to rights to use water from different classes of watercourses.
Water Hammer. The phenomenon of oscillations in the pressure of water in a closed
conduit, flowing full, which results from a too rapid acceleration or retardation or flow.
From this phenomenon, momentary pressures greatly in excess of the normal static
pressure may be produced in a closed conduit.
Water Meter. A device installed in a pipe under pressure for measuring and registering
the quantity of water passing through it.