nciple on which
this pump works. At some point, it may be three or four hundred feet
below the surface of the ground, a valve _A_ opening upward is set in
the well so that it is always submerged. Just above this is a second
valve fastened to the lower end of the long pump rod which reaches up to
the engine or windmill which operates the pump. At each up stroke water
is lifted by the closed valve _B_ and sucked through the open valve _A_.
At each down stroke, the water is held by the closed valve _A_ and
forced up through the open valve _B_.

[Illustration: FIG. 23.--Pump installation.]

The other method of developing a greater quantity of water from a deep
well is to use air pressure to force the water either the entire
distance to the tank or to a point where the suction of an ordinary pump
can reach it, as indicated in Fig. 23. In this method an air blower is
needed, and since this means an engine for operation, it is not
generally feasible, but is suited to occasional needs, where an engine
is already installed for other purposes and is therefore available.

The operation is very simple. An air pipe leads from a blower and
delivers compressed air at the end of the air pipe, which must be below
the level of the water in the well. The pressure of the air then causes
the water to rise, the distance depending on the pressure at which the
air is delivered.

CHAPTER VI

_SOURCES OF WATER-SUPPLY_

Having arrived at the quantity of water necessary to supply the needs of
the average household, we must next investigate the possible sources
from which this quantity can be obtained. Before the advantages of
running water in the house are understood, a well is the normal and
usual method of securing water, although in a few cases progressive
farmers have made use of spring water from the hillsides. It is rare,
indeed, for surface water, so called, to be used for purposes of
water-supply until after modern plumbing conveniences have been
installed. Then the use of surface water becomes almost a necessity
because of the large volume of water needed. The only drawback to its
use is its questionable quality. Without modern plumbing, a well meets
the requirements of family life, but does not answer the demands of
convenience. With modern plumbing, a well is found to be pumped dry long
before the domestic demands are satisfied. The result is an attempt to
secure an unfailing supply, and for this a surface supply is sough