roughly protected, although there are several
hundred privies on the watershed.

Cesspools, in general, are not dangerous if they are located fifty feet
or more from the stream and if no overflow occurs.

Barnyards ought not to drain directly into streams, but when, as in so
many cases, the stream flows through the barnyard, the only remedy is to
move either the stream or the barnyard, and it is difficult to persuade
even a well-disposed neighbor to do either. It is sometimes possible to
appeal to his sense of right; but, too often, the neighbor feels that it
is his land, his barn, his drain, even his brook, and he will do
whatever he pleases with them, whether the water further down stream is
to be used for drinking purposes or not. The question resolves itself
into an inspection of the watershed and a determination of the existing
conditions. If those are tolerable, the water may be used. If evident
contamination is present, the water must usually be given up, and some
other source of supply sought.

_Well water._

The pollution of wells, if it exists at all, is usually very pronounced,
and it is probably safe to say that, except where buildings, drains, or
cesspools have been crowded too close to wells, or where some manifest
and gross cause of pollution exists, a well water is safe to drink.

To protect properly a well from gross pollution, two precautions should
be observed. The wall of the well should be built up in water-tight
masonry, so that surface wash cannot enter the well except at a depth of
at least six feet, and second, this water-tight masonry should be
carried above the surface of the ground at least six inches and the well
then covered with a water-tight floor so that no foreign matter can drop
through the floor into the well or can be washed in by the waste water
from the pump (see Figs. 28, 29, 30). If these precautions are taken, it
is safe to say that nine tenths of the pollution occurring in isolated
wells would be stopped.

Besides the above, a well may be polluted by a stream of underground
water washing the contaminating matter through the soil. Experiments
have been made to show this very plainly. A large number of bacteria
were placed six feet below the surface just in the top of the
underground stream of water. Within a week they were found in
considerable numbers in the water of the soil one hundred feet distant,
but when the same number of bacteria were placed in the soil four feet