80 
IOWA ACADEMY OF SCIENCES. 
is frequently traced the source of contagion. This latter 
declaration applies directly to rural districts, where milk 
cans washed with polluted well water take on germs of 
disease, which are conveyed to the city in the milk. The 
fact that the city water is no conveyor of disease is due to 
careful watching, filtration and thorough and frequent 
cleansing of the filter beds. Through such methods 
epidemics may be averted. 
The Cedar river, which flows through the city, has 
volume and velocity sufficient to keep it comparatively 
pure and to prevent the formation of stagnant pools. In 
fact, the Cedar river is noted for an absence of stagnation. 
The w^ater, soft in quality, is free from excesses of lime 
and magnesia. 
Our artesian water is furnished by three wells, each 
about 1,500 feet deep. Water from this source is hard 
being heavily charged with bi-carbonate of lime and 
bi-carbonate of magnesia. 
Ordinarily about one-fifth of our city water is artesian 
water, the remaining four-fifths being purified river 
water. 
The artesian water is of such a character as to react 
chemically on the river water when a small amount of 
coagulant is used to give a remarkably clear and sparkling 
product. 
Cedar Rapids is exceptionally fortunate in possessing 
such a unique combination of hygienic and economic 
agencies. 
The filtration plant consists of twelve tanks, each four- 
teen feet in diameter, with a capacity of 3,000,000 gallons 
per day. Each tank is thoroughly cleansed twice each 
twenty-four hours by reversing the current of filtered 
water back through the sand and floating the solid matter 
off into the sewers, and also forcing steam through the 
sand to complete cleansing and to sterilize. When mixed, 
the water is forced to the top of the tanks, which contain 
a layer of sand four feet in depth, and by gravity the water 
filters through the sand, leaving the precipitated alumi- 
