248 Bacteriology of Water 



the presenceof micro-organisms of the B. coH group shall not be shown 

 in more than one out of five samples of i o cc. each. There is, however, 

 no formal agreement as to how few or how many colon bacilU shall 

 make the water coiidemnable. It goes without saying that a water 

 without colon bacilli, such as can often be obtained from deep artesian 

 wells is better than surface waters containing a few. How few shall be 

 regarded as consistent with safety remains, at present, a matter of 

 opinion among sanitarians, and varies widely in practice according to 

 the local conditions obtaining in different cities. 



