XVIII. J. M. SMAIL. 



Unflltered water after passing through two 



subsiding reservoirs ... ... ... 177 



A reduction of 88°/°. 



New River Waterworks, Stoke Newington. 



Bacteria per cc. 



New River Out above reservoir ... ... 667 



Outlet of first reservoir 560 



Outlet of second reservoir ... ... ... 183 



Reduction of 72 



Apart from the reduction of bacteria by mechanical 

 sedimentation of mineral matter, it is possible that the 

 bacterial action of the harmless species under the influence 

 of sunlight and air may cause a great reduction in the 

 number and vitality of the harmful bacteria. The percen- 

 tage of reduction would fix the amount of storage necessary, 

 it is obvious that as the matter in suspension varies in 

 different rivers the storage necessary can only be determined 

 by actual experiment with the water to be treated. 



The author had an opportunity of inspecting the large 

 storage reservoirs in course of construction at Staines, 

 England, for the West Middlesex, Grand Junction and New 

 River Waterworks Companies conjointly. The water is 

 taken from the Thames at about 300 yards above the Bell 

 Weir, and conducted to the reservoirs by conduits open 

 and covered, and steel mains to the pumping station, from 

 which it is pumped by five triple expansion Worthington 

 engines to the reservoirs. The reservoirs are about 1\ 

 miles long by | mile wide at northern end, and nearly a 

 mile wide at southern end. The average depth of water 

 in reservoirs is 30 feet, and the capacity is equal to 3,300 

 million gallons. These immense reservoirs as well as stor- 

 iug water will act as sedimentation reservoirs before passing 

 into the companies' filters. The longer the period allowed 

 for sedimentation the better for subsequent filtration and 

 lessening the cost of cleaning the filters, but it is obvious 



