The Bacteria in Natural Waters. 



II 



REDUCTION OF BACTERIA IN WASHINGTON RESERVOIRS. 

 BACTERIA PER C.C. MONTHLY AVERAGE, 1907. 



When the water which enters a pond or a reservoir has 

 abready undergone considerable storage an'd reached a 

 comparatively stable condition, the diminution due to 

 additional storage may be almost neghgible. Thus 

 Philbrick (1905) found that the influent water of the 

 Chestnut Hill Reservoir of the Metropolitan Water Works 

 contained on the average, during the eleven years, 1893- 

 1903, 220 bacteria per cc, and the effluent 179. In many 

 individual months, and in some whole years, the effluent 

 contained more than the influent. 



The seasonal' variations in the bacterial content of a 

 large pond or lake follow a somewhat different course from 

 those observed in a stream. Philbrick, in the paper just 

 cited, gives the figures tabulated on following page for 

 the Chestnut Hill Reservoir of the Metropolitan Water 

 Works (Boston). The averages are based on weekly 

 analyses covering the eleven years, 1 893-1 903. 



