166 UNIVERSITY OF WISCONSIN STUDIES 



Table II includes the unsatisfactory supplies found during 

 the same period. An analysis of this table covering the un- 

 satisfactory supplies shows that 354, or 49 per cent were found 

 to be unsafe by both the field survey and the analytical re- 

 sults; 338, or 46 per cent, by the field survey alone, while 

 the analytical results on the date of the investigation were 

 satisfactory; and 38, or 5 per cent, by the analytical results 

 alone where the field survey did not show the possibilities for 

 pollution and further investigation was required to find the 

 avenues through which pollution could enter the supply. 

 These results show that the field survey was corroborated by 

 the analytical results in 49 per cent of the cases; that the 

 field survey was the only index of danger in 46 per cent ; and 

 the analytical results the only indication in 5 per cent. These 

 results demonstrate the importance of thorough field survey 

 work, for had the analytical results been accepted as the 

 only index, 49 per cent of the unsatisfactory supplies would 

 have been approved. It is also true that if the analytical 

 work had been omitted, 5 per cent of the unsatisfactory sup- 

 plies would have been overlooked. 



It is evident from these results that both field and analytical 

 investigations should be made in order to determine the safety 

 of a water supply from a sanitary point of view. It should 

 be appreciated that the use of any method which permits the 

 collection of haphazard information by untrained individuals 

 is exceedingly dangerous. 



The field survey should give an accurate idea of the possi- 

 bilities of present and future pollution. The analytical re- 

 sults should provide information on the sanitary condition 

 of the water at the particular time the investigation is made 

 and it may supply some information of its past history. The 

 field survey and analytical results combined should afford 

 information on which recommendations can be made for the 

 protection or the abandonment of an unsafe supply. The cor- 

 rective recommendations are frequently very simple and a 

 water supply can be made safe at a relatively small cost. 



In order to illustrate the importance of thorough investiga- 

 tion work, especially in regard to the field survey, it may be 



