Abundant water is rarely reached at less than 75 feet, and it would
usually be impossible to drive a pipe to such a depth. When a large
quantity of water is desired, strong machines drill into the ground
and excavate an opening into which a wide pipe can be lowered. I
recently spent a summer in the Pocono Mountains and saw such a well
completed. The machine drilled to a depth of 250 feet before much
water was reached and to over 300 feet before a flow was obtained
sufficient to satisfy the owner. The water thus obtained was to be the
sole water supply of a hotel accommodating 150 persons; the proprietor
calculated that the requirements of his guests, for bath, toilet,
laundry, kitchen, etc., and the domestics employed to serve them,
together with the livery at their disposal, demanded a flow of 10
gallons per minute. The ground was full of rock and difficult to
penetrate, and it required 6 weeks of constant work for two skilled
men to drill the opening, lower the suction pipe, and install the
pump, the cost being approximately $700.

[Illustration: FIG. 142.--Showing how drinking water can be
contaminated from cesspool _(c)_ and wash water _(w)_.]

The water from such a well is safe and pure except under the
conditions represented in Figure 142. If sewage or slops be poured
upon the ground in the neighborhood of the well, the liquid will seep
through the ground and some may make its way into the pump before it
has been purified by the earth. The impure liquid will thus
contaminate the otherwise pure water and will render it decidedly
harmful. For absolute safety the sewage discharge should be at least
75 feet from the well, and in large hotels, where there is necessarily
a large quantity of sewage, the distance should be much greater. As
the sewage seeps through the ground it loses its impurities, but the
quantity of earth required to purify it depends upon its abundance; a
small depth of soil cannot take care of an indefinite amount of
sewage. Hence, the greater the number of people in a hotel, or the
more abundant the sewage, the greater should be the distance between
well and sewer.

By far the best way to avoid contamination is to see to it that the
sewage discharges into the ground _below_ the well; that is, to dig
the well in such a location that the sewage drainage will be away from
the well.

In cities and towns and large summer communities, the sewage of
individual buildings drains into common tanks ere