WATER IN THE BODY. 171 



cistern, it makes good drinking-water. Falling upon the 

 earth the rain-water soaks down until stopped by some im- 

 pervious layer, such as clay. This water is the supply of our 

 wells and springs. It always has more or less earthy matter 

 in solution, and is therefore called more or less " hard." Un- 

 less a good deal of mineral matter or some special material is 

 dissolved in it, it is ordinarily good drinking-water. Such 

 water is not pure, in the strict sense of the word, but is pure 

 for drinking purposes. 



The great source of danger is from what are called " or- 

 ganic " impurities. Most bacteria will not live and grow in 

 pure water. They must have something on which to feed 

 and grow. But in water containing a good deal of decaying 

 animal or vegetable matter they are likely to abound. And 

 the most dangerous sources of contamination are cesspools and 

 sewers. Water may be contaminated by such material and 

 not have bacteria in it, but is very likely to harbor such foes. 

 The ordinary cesspool is a grave source of danger. Because 

 a well may be on higher ground than the cesspool does not 

 give assurance that the water may not be polluted. Often 

 when the surface of the ground slopes in one direction, the 

 strata underneath may slope in just the opposite direction, 

 and the well may be the reservoir into which the cesspool is 

 drained. 



Good authorities say that a cesspool should not be allowed 

 within a hundred feet of a well. 



But it is better and safer to have no cesspool. Where a 

 sewer system is not to be had, it is better to allow no great 

 accumulation of such material. A deep pit in which a quan- 

 tity of semi-liquid matter gathers is not only a nuisance, but a 

 source of danger. Privies should have a very shallow pit, or 

 none, and should be cleaned often, and the contents disin- 

 fected before they are scattered abroad to endanger the lives 



