WATER SUPPLY AND SEWAGE DISPOSAL 169 



current now flows from the lake into the mouth of the river 

 and up the South Branch, where it enters a new canal, known 

 as the sanitary or drainage canal, thus reversing the recent 

 course of the river. In this way part of the water of Lake 

 Michigan, the normal outlet of which is through the St. 

 Lawrence system, now flows into the Gulf of Mexico and 

 carries with it the sewage of Chicago. In prehistoric times 

 Lake Michigan stood at a higher level, and its waters emptied 

 into the Mississippi system along the route now followed by 

 the drainage canal. 



The construction of the sanitary canal cost more than 

 $56,000,000. The city health department reports that during 

 the ten years before the opening of the canal, in 1900, the 

 average annual death rate from typhoid fever was 66.8 per 

 100,000, but in the ten years following, the rate was -only 

 22.3. It is calculated that this represents a saving of 8814 

 lives. Each life has a money value, dependent upon earning 

 capacity. The health department has calculated that the 

 actual money value of these lives to the community was 

 nearly $53,000,000. In other words, the canal almost paid 

 for itself in the first ten years. It will always pay any city 

 to secure pure water at any necessary cost. 



182. Sewage treatment. The common method of disposing 

 of sewage and other wastes by discharging them into streams, 

 lakes, or ocean is obviously highly objectionable, and the nui- 

 sance tends to increase with the growth of population. At 

 many places it has become necessary to treat the sewage in 

 a manner that will remove its objectionable qualities before 

 allowing it to enter the watercourses. This is usually accom- 

 plished by bacterial action and filtration. Chemical treatment 

 may be used, also, to destroy bacteria. Sometimes the sewage 

 is used to irrigate land. 



183. Rural water supplies. The water supply of farms 

 and villages does not usually receive so much attention as 

 that of cities. Most of the inhabitants of a city secure their 



