RESERVOIRS FOR DRY-FARMING 337 
The rainfall also in many districts comes most largely 
at seasons of no or little plant growth. Reservoirs 
must, therefore, be provided for the storing of the 
water until the periods when it is demanded by 
crops. Cement-lined cisterns are quite common, 
and in many places cement reservoirs have been 
found profitable. In other places the occurrence of 
impervious clay has made possible the establishment 
and construction of cheap reservoirs. The skillful 
and permanent construction of reservoirs is a very 
important subject. Reservoir building should be 
undertaken only after a careful study of the prevail- 
ing conditions and under the advice of the state or 
government officials having such work in charge. 
In general, the first cost of small reservoirs is usually 
somewhat high, but in view of their permanent serv- 
ice and the value of the water to the dry-farm they 
pay a very handsome interest on the investment. 
It is always a mistake for the dry-farmer to postpone 
the construction of a reservoir for the storing of the 
small quantities of water that he may possess, in 
order to save a little money. Perhaps the greatest 
objection to the use of the reservoirs is not their 
relatively high cost, but the fact that since they are 
usually small and the water shallow, too large a pro- 
portion of the water, even under favorable conditions, 
is lost by evaporation. It is ordinarily assumed 
that one half of the water stored in small reservoirs 
throughout the vear is lost by direct evaporation. 
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