Encyclopedia of Environmental Science and Engineering, Volume I and II

WATER TREATMENT 1313

as hardness. One of the major disadvantages of

wells is that they cannot be observed and there-

fore must be considered as somewhat unreliable.

Frequently it has been experienced in the coun-

try, if a drought has persisted for a few days or a

few weeks (depending on the environment) and

the well has been pumped unusually hard, that the

well will run dry. There is never very much warn-

ing of this kind of occurrence and therefore for a

municipal supply it has the distinct disadvantage

of being considered somewhat unreliable.

2) Springs are similarly unreliable, and have a fur-

ther disadvantage in that they require a rather

elaborate engineering system to capture them and

concentrate them into one manageable system.

Also, springs require rather a large protected area

to ensure that man does not pollute this environ-

ment, thereby rendering the springwater unsafe.

3) Rivers tend also to be a little unreliable, although

they do have the advantage that they can be

observed and to some extent controlled through

dams and other waterflow structures. Thus it can

be seen, if the water level is falling, that a munici-

pality may wish to impose water use restrictions

to conserve water until such time as further aug-

mentation of the supply is received through the

hydrologic cycle. One of the major problems with

a river source is that there is a considerable varia-

tion in the quality of the water. During the high

flow flood period, there is frequently a consider-

able amount of silt and organic material which

is washed off the ground, whereas at other times

of year the water may be relatively clean and

require remarkably little treatment prior to distri-

bution. This of course means that water treatment

facilities must be installed to deal with the worst

possible condition, and at other times of the year

it may not in fact be necessary and therefore the

equipment lies idle.

4) Lakes and manmade reservoirs, due to the nature

of flow through them, have a certain stability

both from the point of view of quantity and qual-

ity. Undoubtedly, water coming from a lake or a

reservoir would require far more elaborate treat-

ment than would water from a well. However,

the extreme reliability and the predictability of

supply may well outweigh the considerations of

cost of treatment. This of course is subject to an

economic feasibility study.

5) Oceans. A good deal of attention is currently

being focused on the desalination of ocean water,

and some attention will be paid to this subse-

quently in this section. It should, however, be

remembered that the ocean is only, economi-

cally available to these communities which are

immediately adjacent to the ocean. This leaves a

very large area of hinterland in most continents

which does not have access to the sea. Thus the

Precipitation

Surface runoff

Infiltration

Percolation

Transpiration Evaporation

Snow

Ground water table (G.W.T)

Spring

Lake Swamp

River

G.W.T Ocean

Ground water

From land and water surfaces

=Surface runoff and ground-water runoff

Runoff or stream flow

FIGURE 1 Hydrologic cycle (Fair and Geyer, Water Supply and Wastewater Disposal).

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