agents, and radioactive contaminants which make
it unfit for human consumption and many other
uses. Potable water may or may not be palatable.
Rate of Flow - The volume of water per unit of time
which is passing a certain observation point at a
particular instant. Common expressions are cubic
feet per second, gallons per minute, gallons per
day, and million gallons per day.
Raw Water - Untreated water; usually the water
entering the first treatment unit of a water
purification unit. Water used as a source of water
supply taken from a natural or impounded body of
water, such as a stream, lake, pond, or ground
water aquifer.
Reverse Osmosis - The application of pressure to a
concentrated solution which causes the passage
of a liquid from the concentrated solution to a
weaker solution across a semipermeable mem-
brane. The membrane allows the passage of the
solvent (water) but not the dissolved solids
(solutes). The liquid produced is a demineralized
water.
Total Dissolved Solids - All of the dissolved solids
in a water. TDS is measured on a sample of water
that has passed through a very fine mesh filter to
remove suspended solids. The water passing
through the filter is evaporated and the residue
represents the dissolved solids.
Turbidity - (1) A condition in water caused by the
presence of suspended matter resulting in the
scattering and absorption of light rays. (2) A
measure of fine suspended matter in liquids. (3)
An analytical quantity usually reported in arbitrary
turbidity units determined by measurements of
light diffraction.
A-2
QM 4922
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