54 



GENERAL SCIENCE 



way into the waters that collect in. surf ace wells. This sew- 

 age is not only poisonous to the system, but it may carry 

 into the well water disease germs such as typhoid. In towns 

 and cities where soils are laden with organic waste material 

 the use of water from surface wells is prohibited. Unless one 

 knows the conditions surrounding a surface well, and some- 

 thing of the strata into which 

 it was dug, it is always wise 

 to regard with suspicion any 

 water taken from it for 

 drink or for use in preparing 

 foods. 



Surface waters sometimes 

 find their way down between 

 layers of rock that are sep- 

 arated by a porous stratum 

 where they collect under the 

 pressure of their own ac- 

 cumulation. Boring down 

 into this water-filled layer 

 may result in a rise of these 

 underground waters to or 

 above the surface of the 

 ground. Such- waters are 

 usually free of organic matter 

 and disease germs by natural 



filtration and aeration, but may hold much mineral matter 

 in solution. 



Where rain water is caught and stored in cisterns, in spite 

 of all precautions more or less of dust and of decaying 

 vegetable matter will be washed from the roofs into the 

 cisterns. The water may acquire a disagreeable odor and 

 taste from the decay of the organic matter present, and be- 

 come more or less dangerous as a drink. This organic 



FIG. 22. Use of chain pumps to 

 aerate cistern water. The inverted 

 metal cups carry air down into the 

 water and liberate it as the cups fill 

 with water at the bottom. 



