SIGNIFICANCE OF COLON GROUP IN WATER 165 



At Washington the most complete slow sand- 

 filtration plant yet constructed has yielded the results 

 tabulated below, for which we are indebted to the 

 courtesy of Mr. F. F. Longley: 



B. COLI IN POTOMAC RIVER AND WASHINGTON FILTER 

 EFFLUENT 



It must be remembered that in the Washington plant 

 filtration is supplemented by thorough sedimentation, 

 preliminary and subsequent. The entire credit for the 

 good effluent obtained is not therefore due to the filters. 

 At Lawrence it has been shown that removal of colon 



