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 j^laces 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. 



