tionable and tending to make the house
appear too high. Whenever gutters are built in driveways or ditches to
intercept water coming down the slopes, a suitable outlet must be
provided to carry the water thus collected either into underground
pipes, by which the water is led to some stream or gulley, or directly
into some well-marked surface depression.

_Ground water._

The soil always contains water at a greater or less depth, and the
elevation of this "ground water," as it is called, varies throughout the
year partly with the rainfall and partly with the elevation of the water
level in the near-by streams.

It is not at all unusual for this ground water to rise and fall six feet
or more within the year, high levels coming usually in the spring and
fall, and low levels in the late summer and winter. It is easily
possible, then, that a house cellar may seem dry at the time of
construction in summer and may develop water to a foot or more in depth
after occupancy. The presence of such an amount of water in a cellar,
whether injurious to health or not, is objectionable, and a subsoil
trench should be provided in order to limit the height to which ground
water may rise.

If a system of drainpipes is led around a house extending outward to
include the surrounding yard, then the ground water will always be
maintained at the level of those pipes, provided the system has a free
outlet. Indeed, the question of an outlet for a drainage system is a
most important factor, and no system of underdrains can be effective
unless a stream or gulley or depression of some kind is available into
which the drains may discharge. It is for this reason, quite as much as
for any other, that the location of a house on a perfectly level bottom
land is objectionable, since the ground there may be normally full of
water with no existing depression into which it may be drained.

In the next chapter the proper method of laying drains close to the
cellar wall, for the purpose of taking away the dampness from those
walls, is described, but another system of drains is desirable, covering
more area and more thoroughly drying the ground, provided the ground
water needs attention at all. These drains should be laid like all
agricultural drainage; and while substitution of broken stone, bundles
of twigs, wooden boxes, or flat stone may be made, the only proper
material to be used is burnt clay in the form of tile. These tiles are
made in a variety of