At the same time, the entire valley, or slope of the mountain, which this stream or lake drains of its surface water, is bought up by the Government, or turned into a forest reserve, so that no houses can be built or settlement of any kind permitted upon it.

It can still be used for lumber supply, for pastures, and, within reasonable limits, for a great public hunting and fishing reserve and camping resort.
[Illustration: A CITY WATER SUPPLY BROUGHT FROM THE FAR HILLS] Almost every intelligent and farsighted town, which has not springs or deep wells, is looking toward the acquirement of some such area as this for its source of pure water.

Many great cities go from thirty to fifty miles, and some even a hundred and fifty miles, in order to reach such a source, carrying the water into the city in a huge water-pipe, or _aqueduct_.

These cities find that the millions of dollars saved by the prevention of death and disease amount to many times the cost of such a system, while the water rents gladly paid by both private houses and manufacturing establishments give good interest on the investment.

Any town can afford to go a mile for every thousand of its population for such a source of water supply as this; and secure, _gratis_, a valuable forest preserve, public park, and beauty spot.[15] Filtration.