The filtration plants owned and operated by large cities are usually
safe; there is careful supervision of the filters, and frequent and
effective cleanings are made. In many cities the filtration system is
so good that private care of the water supply is unnecessary.
71. The Source of Water. In the beginning, the earth was stored with
water just as it was with metal, rock, etc. Some of the water
gradually took the form of rivers, lakes, streams, and wells, as now,
and it is this original supply of water which furnishes us all that we
have to-day. We quarry to obtain stone and marble for building, and we
fashion the earth's treasures into forms of our own, but we cannot
create these things. We bore into the ground and drill wells in order
to obtain water from hidden sources; we utilize rapidly flowing
streams to drive the wheels of commerce, but the total amount of water
remains practically unchanged.
|