170 Kansas Academy of Science. 



of chlorine or minerals as to make it unsuitable; and second, the 

 greater portion of it is at such depths as to be beyond the reach of 

 economic production. It is only that portion of the ground water 

 coming from springs, or that is available by comparatively shallow 

 wells, which has any sanitary significance, and to which we will 

 confine our discussion. 



Ordinarily the amount of ground water available in a community 

 depends upon the annual precipitation. The mean annual average 

 rainfall for the different portions of the United States, as tabulated 

 by the weather bureau, is thirty inches. 



Church estimates that one inch of rain would amount to nearly 

 101 gross tons per acre; or, on a house roof of say 20x30, one inch 

 of rain would amount to about 374 gallons. 



Some one has estimated that one-half of the precipitation finds 

 its way into the streams, finally joining the great ocean. This 

 would give the remaining half of this tremendous annual precipi- 

 tation to be absorbed by the soil or given off by evaporation. 



It is commonly believed by the majority of laymen that rain 

 water is an absolutely pure water, but this belief is erroneous; for 

 the raindrops in passing through the atmosphere wash out and 

 collect enormous quantities of dust, smoke and gases, so that, bac- 

 teriologically speaking, it is exceedingly doubtful whether any rain 

 water is absolutely pure. It is probably true that there would be 

 very little, if any, pollution of rain water to the extent of making 

 it a dangerous pollution. 



As -soon as the rain falls upon the earth it of necessity comes in 

 contact with the gross pollution of the top layers of the soil, which 

 some one has denominated "the living earth," and which, as every- 

 one knows, is teeming with myriads of all sorts of germ life. In 

 the inhabited areas this pollution is of a dangerous sort, as would 

 naturally be expected. 



With the descent of the rain drops into the soil there is carried 

 with it more or less organic and inorganic matter, soluble and in- 

 soluble, and myriads of living and lifeless organisms. As the wa- 

 ter sinks deeper and deeper into the porous soil the insoluble 

 matters, as well as the bacterial contents, are gradually filtered out; 

 the rapidity and degree of filtration depending, of course, on the 

 nature and porosity of the soil. As the filtration process goes on, 

 the water, being robbed of its organic matter, becomes the less able 

 to support abundant bacterial life. 



The average soil under ordinary and uncontaminated conditions 

 is supposed to be practically sterile at a depth of twelve feet; at 



