matter of supreme importance in the water supply, however, is not
whether the water is cheap, but whether it is pure. If refuse from
factories is allowed to drain into a stream, the water becomes loaded
with poisonous chemicals, acids, or minerals. If city sewage or
barn-yards are allowed to drain into it, the germs of typhoid and other
fevers enter the water supply. To insure the purity of water supply from
a stream, no factory waste, city sewage or country refuse should be
allowed to enter any part of the stream. In addition to this it should
be carefully filtered.

The disposal of waste is a serious problem, and the easiest way is to
divert it into the nearest water course and trust to the old maxim,
"Running water purifies itself."

This, while true as a general fact, has so many exceptions that it is
not safe to trust to it. The Sanitary District Canal of Chicago has
proved positively that even the most heavily germ-laden water becomes
pure by running many miles at a regulated speed through the open
country, but the conditions are altogether different from those of an
ordinary river. First, in a river, sewage may enter at any point
down-stream to add to the germs already present in the water, while
nothing is allowed to enter the Drainage Canal after it leaves the city.
Second, some germs live for several days and may be carried many miles.
Only a microscopic test can prove whether water contains such germs.
Usually such tests are not made and water is used without people knowing
whether it is pure or not, but the water of the Sanitary Canal is tested
at many points to determine its purity. Each hour and each mile of its
journey it grows purer. This proves that although running water does
purify itself, a stream that is drained into all along its course is not
a fit source of water supply.

Factory refuse, instead of being allowed to pollute the waters, should
be turned to good use by extracting the chemicals, which form valuable
by-products. All farm waste should be taken to a remote part of the
farm, placed in an open shed or vat with cement floor and screened from
flies to form a compost heap for fertilizers for the farm. This will
amply repay the extra trouble and expense by increasing the farm crops.
The sooner such refuse, especially manure, is returned to the land, the
more valuable it is as a fertilizer.

In cities the sewage should be disposed of in such a way as to yield a
profit to the city, and also