MUNICIPAL WATER SUPPLIES. 105 



second, the chemical examination, and third, the bacteriolo- 

 gical examination. Let us consider them one by one. 



The Watershed. — In the examination of the probability 

 of a given watershed furnishing a proper supply of water, 

 good, common sense is perhaps of more avail than scientific 

 knowledge. It is necessary that every springhead and brook 

 contributing to the supply be examined, in order to be assured 

 .that no underground source of contamination is tainting the 

 water from its start. Again, each stream must be followed 

 down to the compounding reservoir and its various sources of 

 sewage and other contamination noted. This is a work of 

 large proportion and great importance. 



Naturally, in the examination of the watershed many 

 voidable and unavoidable sources of infection will be found. 

 The result of the examination will be the knowledge that the 

 supply is subjected to innumerable sources of contamination, 

 and it becomes a most difficult problem to decide whether this 

 contamination is sufficient to condemn the water. Compari- 

 son with other more or less similar water supplies in practical 

 daily use will go far toward solving the question. When, 

 however, this and common sense fail, recourse must be had 

 to chemical and bacteriological examinations. It must be 

 borne in mind, also, that with the natural increase in popula- 

 tion on the watershed the points of infection increase in 

 number. Hence, in passing upon a given supply, some provi- 

 sion for the future must be made and the present day supply 

 must be more than just acceptable. It is to be hoped that 

 legal requirements in the future may do much to alleviate 

 future increase of contamination. Nevertheless some increase 

 is unavoidable and the best we can hope for is that future 

 improvements in the methods of water purification may 

 offset this. 



The Chemical Examination. — The chemical analysis of 

 the water from a given watershed is limited usually to the 

 determination of the following quantities : — Albuminoid 



