50 CHEMISTRY OF FARM PRACTICE 



is more often spread by milk than by water; and cholera, 

 dysentery, and cholera infantum are carried by milk to 

 some extent. Enteric fever is carried by flies. Each of 

 the above-mentioned diseases is spread by as pecific organ- 

 ism, and this organism must first get into the water for 

 the water to become a carrier of the disease. 



It has been estimated that approximately one-third of 

 the water that falls runs off on the surface of the ground 

 into streams. This water is termed the run-off. Two- 

 thirds sinks into the soil, and of this, approximately one- 

 half, or one-third of the total water, is lost by evaporation. 

 This is termed the fly-off. The remainder, approximately 

 one-third of the total rainfall, finds its way out in springs 

 or through subterranean passages. This is termed the 

 cut-off. The proportion of the run-off, fly-off and cut-off 

 will vary with differing conditions, but the above esti- 

 mate is generally approximately true. The cut-off is the 

 water that interests us from the standpoint of sanitary 

 water for rural homes. 



Farm homes are usually supplied with water from one 

 of three sources: springs, shallow wells, or deep wells. 



(a) Spring water is contaminated, and may be infected, 

 by coming in contact with filth of any kind ; for this reason 

 the water-shed of the spring should not have on it, draining 

 toward the springs, any barnyards, pigsties, privies, slaughter 

 houses, or graveyards. The spring should be well ditched 

 around, so as to prevent its being overflowed, contaminated, 

 and possibly infected. It is generally believed that the 

 flowing of water through the soil purifies it, but this de- 

 pends upon the character of the ground through which 

 it flows. Under certain conditions (from a pathogenic 

 standpoint) old water may be better than fresh water, 

 because the germs have had time to die. 



(6) Shallow wells have been used as a source of water- 

 supply since Biblical times. They are likely to become 

 infected through seepage and incomplete filtration. The 



