140 MICRO-ORGANISMS IN WATER 



number of micro-organisms had only been in operation 

 for one day, showing that it had not yet settled down 

 into the normal condition of efficiency which charac- 

 terised the other beds. The number of micro-organisms 

 in the united water from all the filters was only 10 per 

 cubic centimetre. The figures also! show the remark- 

 able diminution in the number of micro-organisms in 

 the unfiltered water by passing through the two large 

 storage reservoirs. 



Uast London Watenvorks, Lea Bridgej Se])temher 2, 1892 

 Filtered Water 



There are no less than 24 filter beds at these works, 

 but they are unfortunately so arranged that it is im- 

 possible to obtain samples representative of the water 

 coming from any one of them singly. Samples were 

 taken from the three wells, in each of which the water 

 from a group of filters is collected. The average 

 number of micro-organisms in the filtered water was 

 very small, and am.ounted to only 18 per cubic centi- 

 metre. The unfiltered water supplying the filter beds 

 contained 676 in the same volume. This unfiltered 

 water was derived from the large storage reservoirs at 

 Walthamstow, and the comparatively small number of 

 micro-organisms which it exhibits shows that a very 

 considerable reduction in the suspended bacteria must 

 have taken place during the storage in those reservoirs, 

 for the water of the Lea itself at the intake must cer- 



