Precipitation. (1) The total measurable supply of water received directly from clouds,
as rain, snow, hail, and sleet; usually expressed as depth in a day, month, or year, and
designated as daily, monthly, or annual precipitation. (2) The process by which
atmospheric moisture is discharged onto a land or water surface. (3) The phenomenon
which occurs when a substance held in solution in a liquid passes out of solution into
Pressure. (1) The total load or force acting upon a surface. (2) In hydraulics the term
when used without qualifications usually means pressure per unit area (pounds per
square inch, or kilograms per square centimeter) above local atmospheric pressure.
Pressure, Atmospheric. The pressure exerted by the atmosphere at any point. Such
pressure decreases as the elevation of the point above sea level increases. One
atmosphere is equal to 14.7 pounds per square inch, 29.92 inches or 760 millimeters of
mercury column or 33.90 feet of water column at average sea level under standard
conditions. Also called standard atmospheric pressure and standard pressure.
Pressure, Hydrostatic. The pressure, expressed as a total quantity or per unit of area,
exerted by a body of water at rest.
Pressure, Negative. A pressure less than the local atmospheric pressure at a given
Pressure Tank. A tank used in connection with a water distribution system, either for a
single household or for several houses, which is airtight and holds both air and water,
and in which the air is compressed, the pressure so created being transmitted to the
Primacy. A state government has primary enforcement authority under the Safe
Drinking Water Act. Primacy is delegated to the state by the Environmental Protection
Agency (EPA) Administrator. Before assuming primacy, the state must establish
drinking water regulations no less stringent than the present National Interim Primary
Drinking Water Regulations (NIPDWR).
Primary Regulations. Regulations governing constituents that affect the health of
consumers are applicable to all public water systems and are enforceable by
Environmental Protection Agency (EPA) or states with primary enforcement authority.
Priming. (1) The action of starting the flow in a pump or siphon. (2) The first coat
applied to a surface to prevent corrosion or to protect the surface.
Public Water System. A system for the provision to the public of piped water for human
consumption, if such a system has at least fifteen service connections or regularly
serves an average of at least 25 individuals daily at least 60 days out of the year. Such