Environmental Engineering Reference
In-Depth Information
Figure 5.1
Machu Pichu, Peru. (Photograph by F.R. Spellman.)
of public water supply systems is tied directly to the growth of cities. In cases
where a surface water source was not available, settlers dug wells to supply
water to community residents.
A typical water supply system consists of six functional elements: (1) a
source or sources of supply; (2) storage facilities (e.g., impoundment reser-
voirs); (3) transmission facilities to transport water from the point of stor-
age to the treatment plant; (4) treatment facilities for altering water quality;
(5) transmission and storage facilities for transporting water to intermediate
points (such as water towers or standpipes); and (6) distribution facilities for
bringing water to individual users (see
Figure 5.2
).
Recall that when precipitation falls on a watershed or catchment area, it
either flows as runoff above ground to streams and rivers or soaks into the
ground to reappear in springs or where it can be drawn from wells. A water
supply can come from a catchment area that may contain several thousands
of acres (or hectares) of land, draining to streams whose flow is retained in
impoundment reservoirs. If a water supply is drawn from a large river or
lake, the catchment area is the entire area upstream from the point of intake.
Obviously, the amount of water that enters a water supply system depends
on the amount of precipitation and the volume of the runoff. The annual aver-
age precipitation in the United States is about 30 inches, of which two-thirds
