THE WATER SUPPLY OF LONDON. 165 



be urged against the plan on[ that score ; and with such 

 rapidity as not to interfere with the regularity of service." 



Before the year i82g, therefore, the river water supplied 

 to London was not filtered at all ; but after the issue of 

 this report, the Companies set themselves earnestly to work 

 to improve the quality of the water by filtration. 



The first filter, on a working scale, was constructed and 

 brought into use by the Chelsea Water Company in the 

 year 1829. But even as late as 1850 only three out of the 

 seven principal companies filtered the river water which 

 they delivered in London ; and it was not until 1856 that 

 filtration was made compulsory by Act of Parliament, 

 whilst it can scarcely be doubted that, between this date and 

 the year 1868, when my observations on turbidity were first 

 commenced, the operation was very imperfectly performed. 



In the year 1832, and again in 1849, London was 

 severely visited by epidemic cholera, and the agency of 

 drinking water in spreading the disease forced itself upon 

 the attention of the observant portion of the medical pro- 

 fession. It was Dr. Snowe, however, who in August, 

 1849, first formally enunciated the doctrine that drinking 

 water polluted by choleraic matters is the chief mode by 

 which cholera is propagated. 



Received at first with incredulity, this doctrine was 

 supported by numerous facts, and it soon caused renewed 

 attention to be directed to the quality of the water then 

 being supplied to the Metropolis ; with the result that the 

 intakes of the various Companies drawing from rivers 

 were, one after another, removed to positions above the 

 reach of tidal influence ; the Thames water being with- 

 drawn from the river above Teddington Lock, and the Lea 

 water at Ponder's End, above the tidal reaches of that river. 



In every visitation of Asiatic cholera to London, the 

 water supply was either altogether unfiltered or imperfectly 

 filtered, besides being derived from highly polluted parts 

 of the Thames and Lea ; and the enormous loss of life, 

 amounting in the aggregate to nearly 36,000 people, can 

 only be attributed to this cause. It has been abundantly 

 proved that efficient filtration is a perfect safeguard against 



