and the Storage of Water. 
41 
storage room adapted for the same period. On the eastern side 
of England, Mr. Hawkesley states that periods have occurred 
where, in dry seasons, 250 days have elapsed from the first 
lowering of the water in the reservoirs to the commencement ot 
its re-elevation.* Speaking generally, storage for 150 to 180 
days will be found sufficient. The quantity of rain to be 
depended on in dry seasons may be ascertained by finding the 
average fall of the district and deducting one-sixth, the result 
almost as an invariable rule giving the available rainfall of three 
consecutive minimum years. Taking, as before, 22 inches as the 
average rainfall, the quantity to be relied on would be 16 inches. 
From this must be deducted the loss from evaporation and 
absorption by vegetation, &c., which varies from 10 up to 18 
inches in extreme cases. The mean may be taken at 14 inches, 
leaving only 2 inches to be stored. This rainfall on an acre of 
drained land will yield 45,229 gallons (7260 cubic feet). The 
superficial dimensions of the reservoir will depend on the supply 
required ; the depth, however, ought not to be less than from 6 
to 7 feet, as with this depth there will be less loss from evapora- 
tion and the water will keep better. In retentive clay soils, it 
may be found sufficient merely to form the reservoir in the soil 
by excavation ; but where the strata are porous, the sides and 
bottom must be puddled, or lined with concrete or brickwork. 
In the latter case the excavation will not require to be carried 
the full depth of the reservoir, the walls being built partly above 
the surface and being backed up with the excavated material. 
A small village, with mansion, vicarage, gardens, stables, farm- 
steads, and cottages, would require about 2,000,000 gallons of 
water in the course of the year, and, allowing storage for 180 
days, would require a reservoir 7 feet deep and about 150 feet 
square, and a gathering ground of 50 acres. The cost of supply 
from such reservoirs to villages may be taken roughly at from 
20s. to 25s. a head of the population. Mr. Bailey Denton calcu- 
lates that 1 inch of rainfall on an acre would supply two and 
a-half persons with water for a year, at the rate of 25 gallons 
each.f At this rate, 120 acres would be required instead of 50. 
This outline of the requirements of village water-supply is 
sufficient to give a general idea of what is necessary. The special 
means to be adopted in any particular locality must depend upon 
the circumstances of the district : no scheme generally applicable 
can be laid down. 
A typical case, showing how easy it is for a private indi- 
vidual to carry out works of water-supply, will be found in the 
* "Water Supply, Paisley," ' Trans. Instit. Civil Engineers,' vol. xxxi. 
t ' Storage of Water.' By B. Denton. Spon and Co., 1874. 
