Two Possibilities

The Water Problem of a Large City:
Sometimes a city is fortunate enough to be situated near hills and mountains through which streams flow, and in that case the water problem is simple. In such a case all that is necessary is to run pipes, usually underground, from the elevated lakes or streams to the individual houses, or to common reservoirs from which it is distributed to the various buildings.

Figure illustrates in a simple way the manner in which a mountain lake may serve to supply the inhabitants of a valley. The city of Denver, for example, is surrounded by mountains abounding in streams of pure, clear water; pipes convey the water from these heights to the city, and thus a cheap and adequate flow is obtained. Such a system is known as the gravity system. The nearer and steeper the elevation, the greater the force with which the water flows through the valley pipes, and hence the stronger the discharge from the faucets.

Relatively few cities and towns are so favorably situated as regards water; more often the mountains are too distant, or the elevation is too slight, to be of practical value. Cities situated in plains and remote from mountains are obliged to utilize the water of such streams as flow through the land, forcing it to the necessary height by means of pumps. Streams which flow through populated regions are apt to be contaminated, and hence water from them requires public filtration. Cities using such a water supply thus have the double expense of pumping and filtration.

FIG. - The elevated mountain lake serves as a source of water.