WATER FILTRATION. XXIX. 



that to maintain a high bacterial standard the rate of filtra- 

 tion must not exceed 4 lineal inches per hour, or practically 

 2 gallons per square foot per hour — or rather more than one 

 million gallons per acre. It is essential that this should 

 not be exceeded, and that the controlling appliances should 

 be such as to ensure uniformity of work of filtration. 



American Practice. 

 The European system of slow filtration does not appear 

 to be much in evidence in connection with the water supply 

 to the cities in the United States, where water has to be 

 drawn from rivers. Many of the earlier installations were 

 constructed on the European method, but where the water 

 to be treated is very turbid the results have not been satis- 

 factory. 



Mr. John W. Hill, Chief Engineer Bureau of Filtration, 

 is carrying out extensive works in connection with the 

 water supply of Philadelphia on the European system. The 

 total land appropriated for filters and other works totals 

 462*5 acres. The system comprises subsiding reservoirs, 

 preliminary filters, plain sand filters, and clear water basins. 

 The water is drawn from the Schuylkill and Delaware rivers. 

 One section of the system includes a sedimentation reservoir 

 with a capacity of 72 million U.S. gallons, and a system of 

 preliminary filters of daily capacity of 40 million U.S. gallons 

 to be extended to 97 million gallons for future consumption. 

 It will be seen that this system comprises sedimentation 

 and double filtration, and, considering the source from 

 which the water is drawn, this system is obviously neces- 

 sary. The works are in progress, and can only be incident- 

 ally referred to as a type of slow filtration. 



The author had an opportunity of examining another type 

 of slow filtration at Lawrence, Mass. It is of unique con- 

 struction, influenced by the state of the town funds when 

 economy of construction had to be an essential factor. The 



