58 WATER 



water depended upon an efficient soil filtration, and that this 

 might break down at any time and without warning. 



River Water. 



The terms river and stream cover so many conditions 

 which differ very widely that obviously no possible standards 

 can be forthcoming. Rivers, receiving as they do the washings 

 from the lands they flow through, usually show a high bacterio- 

 logical content, and as the land so draining is often cultivated, 

 a high content in excretal indicators such as B. coli and 

 streptococci. Such contaminated waters obviously cannot 

 be considered as satisfactory sources of supply for drinking 

 unless purification has taken place by sedimentation (storage) 

 or filtration. Their bacterial purity can be judged with great 

 accuracy by their content in the B. coli group of organisms. 



Bacterial Standards. 



From the above considerations it will be evident that no 

 very definite bacteriological standards can be framed, even when 

 each class of water is separately considered. At the same time 

 it is quite possible to frame working guides, as indicated above, 

 and if these are used with reasonable care to obtain most 

 valuable opinions upon any given water supply. 



Of the different data available to form such an opinion the 

 B. coli group enumeration is by far the most valuable, the 

 other findings being more or less confirmatory. The above 

 considerations set out as a reasonable requirement that "excretal" 

 B. coli should be absent from 100 c.c. of deep water supplies and 

 from loc.c. of surface waters. 



Sometimes the organisms isolated are not typical B. coli, but 

 differing in the absence of one or more of the characteristic 

 properties of this organism. In the writer's opinion the nearer 

 these lactose-fermenting coli-like bacilli approach typical B. coli 

 in their characters, the more nearly are our numerical standards 

 for that organism applicable to them, while if they lack essential 

 characters a proportionately greater number must be present to 

 justify an adverse opinion. 



