1896.] on the Past, Present and Future Water Sajpply of London. 57 



quality of these waters gradually improved, in this most important 

 res23ect, as is seen from the foregoing diagram. 



These observations, graphically represented in the diagram, show 

 that at the time they were commenced the filtering operations were 

 carried on with great carelessness, and that this continued, though 

 to a less extent, down to the year 1883, since which time, and 

 especially since 1884, the efficiency of filtration of all the river 

 waters su]Dplied to the metroj^olis has left little to be desired. 



What is it, then, that S8j)arates the past from the jDresent water 

 supply of London ? In the first place there is the change of source ; 

 I mean the change in position of the intakes of the several companies 

 drawing from the Thames and Lea, and the total abandonment of 

 the much polluted Eavensbourne by the Kent Water Company. So 

 long as the water supply was derived from the tidal reaches of the 

 Thames and Lea, receiving, as these reaches did, the drainao-e of 

 immense populations, the risk of infection from water-borne patho- 

 genic organisms could scarcely be otherwise than imminent ; for, 

 although we now know efficient filtration to be a perfect safeguard, 

 anything short of efficiency must be attended with risk in the presence 

 of such extreme pollution. 



Nevertheless, the line of demarcation between the past and the 

 present water supply of the metropolis is, in my opinion, to be drawn 

 not when the intakes of the river companies were removed to positions 

 beyond the possibility of pollution by the _ drainage of London; but 

 at the time when efficient filtration was finally secured and ever since 

 maintained ; that is to say, in the year 1884. 



The removal of turbidity by sand filtration, however, refers only 

 to suspended matter, but there are sometimes objectionable substances 

 in solution, of which organic matter is the most important. River 

 water and mountain water, even when efficiently filtered, contain 

 more organic matter than spring or deep-well water ; but this is 

 reduced in quantity by storage and especially by filtration ; although 

 it can, perhaps, never be brought up to the standard of organic purity 

 of spring and deep-well water. 



The Present Water Sujpjply. 



At present, London is supplied with water from four sources, the 

 Thames, the Lea, the New Kiver and deep wells. Of these, the deep 

 wells yield, as a rule, the purest water, requiring no filtration or treat- 

 ment of any kind before delivery for domestic use. The river waters 



on the other hand, require some kind of treatment before delivery ; 



storage and subsidence in reservoirs, and filtration. The water from 

 the Thames is abstracted at and above Hampton, far above the reach 

 of the tide and London drainage. The water from the Lea is taken 

 out at two 'points, viz. at Angel Road, near Chingford, by the East 

 London Water Company ; and above Hertford by the New River 



