All about Water: Basic Concepts - The Drinking Water - page 18

they allot grants and loans for the construction of treatment works.
The Act established national discharge standards with enforcement
provisions and established several milestone achievement dates. It
required secondary treatment of domestic waste by publicly owned
treatment works (POTW) and the application of “best practicable”
water pollution control technology by 1977. Virtually all industrial
sources achieved compliance. (Because of economic difficulties
and cumbersome federal requirements, certain POTW obtained an
extension to July 1, 1988, to achieve compliance.) The Act also called
for new levels of technology to be imposed during the 1980s and
1990s, particularly for controlling toxic pollutants. The Act man-
dates a strong pretreatment program to control toxic pollutants dis-
charged by industry into POTW. The 1987 amendments require that
stormwater from industrial activity must be regulated.
Filtration— A physical treatment method for removing solid (particu-
late) matter from water by passing the water through porous media
such as sand or a manmade filter.
Flocculation— The water treatment process following coagulation; it
uses gentle stirring to bring suspended particles together so they
will form larger, more settleable clumps called loc .
Grab sample— A single water sample collected at one time from a single
point.
Groundwater— The fresh water found under the Earth's surface, usually
in aquifers. Groundwater is a major source of drinking water and a
source of growing concern in areas where leaching agricultural or
industrial pollutants or substances from leaking underground stor-
age tanks are contaminating groundwater.
Hardness— A characteristic of water caused primarily by the salts of cal-
cium and magnesium. It leads to the deposition of scale in boilers,
damages equipment in industrial processes, and sometimes causes
an objectionable taste. It may also decrease the effectiveness of soap.
Hydrogen bonding— The term used to describe the weak but effective
attraction that occurs between polar covalent molecules.
Hydrologic cycle— Literally the water-Earth cycle; the movement of
water in all three physical forms through the various environmental
mediums (air, water, biota, and soil).
Hygroscopic— A substance that readily absorbs moisture.
Inluent— Water flowing into a reservoir, basin, or treatment plant.
Inorganic chemical —A chemical substance of mineral origin not having
carbon in its molecular structure.
Ionic bond— The attractive forces between oppositely charged ions—for
example, the forces between sodium and chloride ions in a sodium
chloride crystal.