made useful and profitable as
is the soil itself.

The amount of water is fixed and passes in an endless round from cloud
to river or land and back to the clouds again. The average yearly
rainfall of the United States is estimated at thirty inches, about forty
inches in the eastern half, an average of eighteen inches in the western
part, and in many places not more than ten or twelve inches. One inch of
rain would amount to nearly one hundred and one tons per acre, or on a
roof twenty feet long by twenty feet wide, one inch of rain would be two
hundred and fifty gallons. With a rainfall of forty inches, this would
amount to 10,000 gallons in a year, or an average, over every bit of
land twenty feet square, of twenty-seven gallons for every day in the
year. This is about the quantity that falls in the eastern part of the
United States.

It varies slightly from year to year, but there is no more--there is no
possible way of adding to it, though we may lessen it by allowing it to
rush out to sea, giving no service to the land. As the land waters
diminish the rainfall also grows less.

This two hundred trillions cubic feet of water which falls on our land
every year constitutes our entire water resource, is the source of all
our rivers and streams, of the moisture in the air, of our rains and
snows, and our water for plant and animal growth.

To understand how much this is, we may say that it is about equal to ten
times the amount of water that flows through the Mississippi River
system. The water of the Mississippi and its branches is nearly half of
all the water in the United States that flows through waterways to the
sea. This water that flows through our streams is sometimes called the
run-off. The run-off is increasing every year as we cut our forests and
cultivate our land. It is used for navigation, irrigation and power, but
the increase is not an advantage for these purposes as might be
supposed, because it comes in disastrous floods, tearing away dams,
ruining power sites, and not only preventing navigation during the flood
season, but by filling up the rivers and changing the channels, making
navigation difficult and dangerous throughout the year. The run-off is
controlled to some extent and may be brought under almost as complete
control as may be desired.

As much as the water of five or six Mississippis, or a little more than
half of our supply, is evaporated to moisten and temper the air, to fall
as rai