CHAS. E. FOWLER. 287 



water in the reservoir to meet such contingencies, but 

 this difficulty always appears at one of the seasons when 

 the daily consumption of water is the greatest and near- 

 est to themaxium capacity of the filters, so that from ten 

 to fifteen days, at the best, are required to till the reser- 

 voir, which would be exhausted in much less than half 

 the time when pumping is discontinued. It sometimes 

 hapi)ens that the algse begins to decrease the delivery 

 from the beds in 48 hours after removal and entirely 

 stops it in seven days, and before we have been able to 

 fill the reservoir to the point where the tirst development 

 began, so that if a succession of these occurrences should 

 happen the supply would be exhausted from this cause 

 alone; but fortunately these extreme instances do not 

 frequently occur in succession. 



The second of the difficulties mentioned, the condi- 

 tions of the weather, sometimes combines with the former 

 to make matters worse. One of the peculiarities of this 

 method of filtration is that the suiface of the sand can- 

 not be cleaned during a storm of any kind. Even if the 

 men could be induced to work it would be of no avail 

 during an ordinary rain storm as the silt and algse, under 

 the action of the rain slip from the Avet shovels only to 

 form a more impervious coat on the cleaned sand. The 

 attempt has been repeatedly made only to find that the 

 work had to be done over again after the rain ceased. It 

 will be understood therefore that if when, by reason of 

 algae growth, we have been compelled to stop filtering, 

 empty and drain the beds for cleaning, thereby reducing 

 the filtered water supply to just enough to last during 

 the operation of cleaning, and a rain storm sets in delay- 

 ing the work, the result must be to entirely exhaust the 

 supply and compel us to pump untiltered water. Ordi- 

 narily, when the cold is severe and continuous, the water 

 in the river is comparatively clear, in fact at its best, and 

 the beds would run for several weeks without clean- 



225 



