Foods and Cooking. 147 



water is pure, and if caught on a clean roof (especially a 

 slate roof) and kept in a clean cistern, it is good drinking- 

 water. 



Well Water. Falling upon the earth, the rain water 

 filters down until stopped by some layer, such as clay, 

 through which it cannot soak. This water is the supply 

 of our wells and springs. It always has more or less 

 earthy matter, especially lime, in solution, and is therefore 

 more or less " hard." Unless a large amount 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. 



Impurities in Water. The great source of danger is 

 from what are called "organic" impurities. Bacteria do 

 not thrive in pure water. They must have something on 

 which to feed and grow. But in water containing a large 

 amount 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. 



Contamination from Cesspools. The ordinary cesspool 

 is a grave source of danger. Because the well may be on 

 higher ground than the cesspool does not give assurance 

 that the water may not be polluted. Often when the sur- 

 face of the ground slopes in one direction, the strata 

 underneath may slope in 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. 



