THE WATER SUPPLY OF LONDON. 



167 



filtered. Previous to the year 1868, there are no records 

 of the efficiency, or otherwise, of the filtration of the 

 Metropolitan water supply derived from rivers, as dis- 

 tinguished from deep wells, the water of which is perfectly 

 clear without filtration. 



It was in the year 1868 that I first began to examine 

 the water supplied to the Metropolis from rivers with 

 reference to efficiency of filtration. I n that year, out of 

 eighty-four samples examined, seven were very turbid, 

 eight turbid, and ten slightly turbid, so that altogether no 

 less than nearly 30 per cent, of the samples were those of 

 inefficiently filtered water. The Metropolitan Water Supply 

 then, up to the year 1868, may be shortly described as 





No. 1. 



derived for many years from very impure sources with 

 either no filtration at all, or with very inefficient filtration ; 

 and afterwards, when the very impure sources were 

 abandoned, the supply was still often delivered in a very 

 inefficiently filtered condition. But, after the establishment of 

 monthly reports on the filtration of the river-derived supplies, 

 the quality of these waters gradually improved in this most 

 important respect, as is seen from diagram No. 1. In this 

 diagram, the continuous line with dots represents the 

 mortality from typhoid in Manchester, the broken and 

 eroped line the contemporaneous mortality in London, and 

 the dotted curve the degree of turbidity of the London 

 water supply. 



