WATER SUPPLIES 467 



Chicago and other cities which once obtained their drinking water 

 from lakes polluted with sewage always had a high death rate from 

 typhoid. In the year 1891, the death rate from typhoid was over 

 170 per 100,000 inhabitants. Today it is less than 3 per 100,000. 

 Olean, New York, had a serious outbreak of 248 cases in the fall 

 of 1928 because one of the shallow wells used by the city became 

 contaminated with sewage from the Allegheny River. It cost 

 the city of Olean $425,000 to pay the cost of the care of the 

 cases and to settle the claims made against the city for its care- 

 lessness. 



Water supplies. By pure water we mean water free from all 

 organic impurities, including disease germs. Water from springs 

 and deep driven wells is the safest water ; that from large reser- 

 voirs next best ; while water that has drainage in it, river water 

 for example, is very unsafe unless properly treated with chemicals. 



The water from deep wells or springs, if properly protected, will 

 contain few bacteria. Water taken from shallow, unprotected 

 wells may have from 100 to 20,000 bacteria per cubic centimeter. 

 Water taken from protected streams into which no sewage flows 

 usually has few bacteria (from 50 to 300 bacteria per cubic centi- 

 meter), and these are destroyed if exposed to the action of the 

 sun and the constant aeration (mixing with oxygen) which the 

 surface water receives in a large lake or reservoir. But water 

 taken from a river into which the sewage of towns and cities flows 

 may contain many hundreds of thousands of bacteria to the cubic 

 centimeter,' and must be filtered and chlorinated before it is fit 

 for use. The water is passed through settling basins and sand 

 filters which remove about 98 per cent of the germs. Final treat- 

 ment with hypochlorite of lime or liquid chlorine in very small 

 amounts kills most of the remaining bacteria. A few fortunate 

 cities, such as Los Angeles and New York, bring their water sup- 

 plies from protected areas far up in the mountains. 



We have already seen the danger of typhoid fever from unpro- 

 tected water supplies. Fortunately most large cities now protect 

 their supplies, either by filtration and chlorination or, as in the 

 case of Chicago, by this means plus a drainage canal which carries 

 off the sewage. 



