The Supply and Uses of Water 211 



matter, that which concerns the individual and the individual 

 family as in rural districts, and that which concerns the entire 

 community or city. In the city, for instance, there is the waste 

 of the household, the factory, and all industrial and commercial 

 institutions. We do not need to consider here the removal of 

 such materials as garbage, ashes, paper, cans, bottles, etc., which 

 are often collected for their commercial value. We have only 

 to consider the methods employed for the disposal of sewage 

 and the ways by which it may be treated to remove all danger 

 to human life and health. 



84. Some ways of sewage disposal for cities. Sewage is 

 frequently turned into a system of conduits and discharged 

 from these wherever sanitary wisdom or often carelessness or 

 false economy may decree. The conduits may be on the sur- 

 face, as in certain parts of South America, Asia, and in some 

 localities in the United States. The only approximately san- 

 itary sewers are placed underground, and are watertight ex- 

 cept for entrance and discharge of sewage or for temporary 

 opening to remove obstacles clogging up the sewers. The 

 sewers must be watertight to prevent pollution of the ground 

 through which the conduits are laid, and also to prevent the 

 entrance of surface drainage and materials that would tend to 

 block the system. The provision of openings at suitable 

 places is necessary to give ventilation and to allow chemical 

 treatment to destroy offensive odors. 



Water is the carrier of sewage in the community as well as in 

 the individual organism. Practically all the water used in a com- 

 munity is turned into the sewage to carry away waste products. 

 Where surface drainage is conducted by gutters and basins into 

 the same system, it helps to flush and prevent the more or less 

 permanent deposits from clogging the pipes. When rainfall is 

 carried off in surface gutters, additional water is necessary at 

 times thoroughly to cleanse the sewer system. This means an 

 increase in the quantity of water consumed and of the water 

 supply ; but it cannot be regarded as waste or extravagance. 



