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 
ficld survey and analytical results combined should afford 
information on which recommendations can be made for the 
protection ov 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 ficld survey, it may be 
