Applied Biology 781 



C. Water Supplies and Sewage Disposal 



Water is an important substance of all living organisms, and many of 

 the activities necessary for their existence are dependent upon the proper 

 quantity and quality of water. The chemical reactions of digestion, 

 growth, and reproduction are dependent upon water, and the enzymes 

 which aid in these processes act in aqueous solutions. Water is essential 

 in the elimination of wastes, regulation of body temperatures, main- 

 tenance of proper consistency of blood, lymph, etc. Water is one of the 

 best solvents for animals and plants as the following suggests: it dissolves 

 soil particles and chemicals for plant use and it dissolves acids, alkalis, 

 salts, gases and many other materials which have an endless variety of 

 uses in the living organism. 



The value of water has been recognized by peoples of all times because 

 they have tended to settle where the supply has been of the proper quan- 

 tity and quality. In the past the quantity and quality were not always 

 the problem which they now are because of greater use of water and 

 greater centers of population, together with increased industrialization. 

 Today in many areas the "water problem" has become acute. Primitive 

 peoples used water for drinking, for preparing food, and a small amount 

 for washing and for their primitive handicrafts. As populations increased 

 and urban industrialization developed, the amount of water required was 

 greatly increased. Today, in some communities, we find water sanita- 

 tion so inadequate that people actually consume their own sewage or 

 that of the neighbor in order to get a sufficient supply. The per capita 

 daily consumption of water in our cities is about 100 gallons, although it 

 runs as high as 250 gallons in certain cities. European cities average 

 only about 50 gallons, with a few using as much as 100 gallons daily. 

 Such factors as the following influence the amount of water consumed: 

 the cost of the water, the number and types of industries, the chemical 

 and physical properties of the water, the amount used in cleaning streets, 

 the number of fires which firemen must put out, whether the water is 

 sold by meter or not, the number of leaky fixtures and pipes, the temper- 

 ature and humidity of the climate, the amount used in watering lawns 

 and gardens, etc. 



Water comes to the earth in rain or snow; some is used by animals 

 and plants and some evaporates, while the remainder collects on the sur- 

 face of the earth or penetrates into the subsurface of the earth. Two 

 sources of water are: surface (rivers, lakes, reservoirs, etc.) and subsur- 

 face or ground (wells, underground rivers and lakes, etc.). Waters may 

 be classified as: (1) potable water, which is safe from the standpoint 



