WATER SUPPLY. 81 



refer to the well at the head of the Serpentine, where the level 

 has fallen 93 ft. in less than 50 years, or those near the National 

 Gallery, where the fall has been 115 ft. in 64 years. 



The quality is normally good, the hardness of water from 

 37 wells in the City varying from 11 to 3*5 degrees, while the 

 total solids average about 49 grains per gallon. 1 It is usually 

 found that the water from wells sunk where the Chalk is near 

 the surface contains a much higher proportion of lime than 

 that from wells sunk through a thick cover of Tertiary Beds. 

 In the latter case much of the water has really come from the 

 Thanet Sand and has exchanged some of its lime salts for those 

 of sodium ; the proportion of salt is, however, much diminished 

 where heavy pumping has continued for some years. Where 

 there is no impervious cover to the Chalk, there is a danger of 

 impure water from the surface gravels or from the Thames being 

 drawn down into the Chalk. 



The water from the river-gravels is in many parts abundant 

 and can be used for certain industrial purposes where slight 

 impurity is of no consequence. In excavations for the extension 

 of the Victoria and Albert Museum in South Kensington more 

 than 10,000 gallons per hour had to be pumped from the gravel. 

 The extent of contamination naturally varies according to the 

 locality. In West Kensington water encountered in making the 

 incline for the Piccadilly Tube was found to be so poisonous that 

 the men engaged on the work had to receive medical treatment 

 for the slightest scratch. 



The rocks beneath the Chalk are not of much value as a 

 source of water around London, except where the Lower Green - 

 sand is present (p. 6), though a well at Mile End obtained half 

 a million gallons per week from the Upper Greensand at a depth 

 of 875 ft. The Devonian rocks, reached by most of the deeper 

 borings, sometimes yield a fairly large supply, but the water is 

 brackish; that from the boring at White Heather Laundry, 

 Willesden, contained as much as 1 5 per cent, of salt. 



The history of the Water Supply of London is of great 

 interest, and a general outline may be given here. Apart from 

 brooks and rivers, the first supply was from springs and shallow 

 wells. Over much of the area of ' Greater London ' river -gravels 

 overlie the impervious London Clay, and under natural conditions 

 contain a certain amount of water. This water appears in 

 springs at the margins of the gravel, more especially where a 

 once continuous spread is cut through by the valley of a little 

 stream, and can be tapped by means of a shallow well (see p. 89). 

 It was on such gravel patches that London itself and the out- 

 lying hamlets, for example, Camberwell, Clapham, Kensington, 

 Paddington and Islington, sprang up. The intervening areas of 

 bare clay were not built upon till the advent of the great Water 

 Companies and the introduction of iron pipes and steam pumping. 



1 Report of the Medical Officer of Health for the City of London, May, 1910. 



