the case with mountain lakes, because they are at
a distance from sources of contamination. The character of the water
depends upon whether the lake is fed by brooks, that is, by the rain
falling upon the watershed, or also by springs. In one case the water
is surface water exclusively; in the other, it is surface and
underground water mixed. The purity also depends upon the depth of
the lake and upon the character of its bottom.

Deep lakes furnish a better supply and clearer water than shallow
ones. The solid matter brought into the lake by the brooks or rivers
which feed it does not remain long in suspension, but soon settles at
the bottom, and in this way some lakes acquire the wonderfully clear
water and the beautiful bluish-green color for which they are far
famed.

_Strong Winds Dangerous on Lakes_

Strong winds or currents at times stir up the mud from the bottom;
hence, in locating the intake, the direction of the prevailing winds
should be considered, if practicable. The suction pipe should always
be placed in deep water, at a depth of at least fifteen to twenty
feet, for here the water is purer and always cooler.

Settlements on the shores of a lake imply danger of sewage
contamination, but the larger the lake, the less is the danger of a
marked or serious pollution, if the houses are scattered and few.

Pools and stagnant ponds are not to be recommended as a source of
supply. In artificially made lakes there is sometimes danger of
vegetable pollution, and trouble with growth of algae. The bottom of
such lakes should always be cleared from all dead vegetation.

Surface water may be obtained from brooks flowing through uninhabited
upland or from mountain streams. Such water is very pure and limpid,
particularly where the stream in its downward course tumbles over
rocks or forms waterfalls. But, even then, the watershed of the stream
should be guarded to prevent subsequent contamination. Larger creeks
or rivers are not desirable as a source of supply, for settlements of
human habitations, hamlets, villages, and even towns are apt to be
located on the banks of the river, which is quite generally
used--wrong as it is--as an outlet for the liquid wastes of the
community, thus becoming in time grossly polluted. Down-stream
neighbors are sure to suffer from a pollution of the stream, which the
law should prevent.

_The Water of Springs_

The water of springs is subterranean, or ground water, which for