STORAGE AND DISTRIBUTION. 



145 



valve, shown in fig. 109, is a useful device for ad- 

 mitting the water evenly over the sand. 



In figs. 1 1 1 and 

 1 12 details are given 

 of a larger and more 

 solid type of under- 

 ground tank than 

 has yet been dis- 

 cussed, for storing 

 clear water from a 

 filter-bed. It will be 

 seen that the tank 

 is partly in cutting 

 only, and that when 

 built the roof is 

 covered with earth 

 and a bank con- FIG. no. 



structed all round. 

 In addition to the side walls, which must withstand 



FIG. in. 



the water thrust and the thrust of the arched roof, 

 there are a series of piers with arches turned 



10 



