CHAPTER V. 



WATER SUPPLY. 



In calculating on engaging in an irrigation enter- 

 prise of any kind it is well to remember that we must 

 first catch our rabbit before we can cook the stew. No 

 one should attempt irrigation without first having 

 determined the extent and continuity of the water sup- 

 ply, and where a vast amount of money will be needful 

 in carrying out the enterprise, as in the construction of 

 large works, the services of a practical hydraulic engineer 

 should be secured by all means, and his report should be 

 rendered before entering upon the scheme. To get at 

 the source of all water supply, we must accept the well- 

 recognized scientific fact that the waters upon the earth 

 and the clouds in the air are forever in reciprocal motion. 

 The waters are lifted and ascend into the heavens, the 

 clouds are drifted away over the land and discharge their 

 moisture upon the land, and life is supported thereby. 

 The amount of water which is taken out of the ocean by 

 evaporation each year is very great. About thirty-five or 

 thirty-six inches of water rises by evaporation from the 

 surface of the earth annually. This rainfall on the entire 

 earth would make a sheet as large as the surface of the 

 earth and about three feet in depth. It would fill Lake 

 Superior six times every year. 



Evaporation and Run-Off. When the rain falls 

 upon the surface of the earth, a part is evaporated ;i:il 

 carried away in the clouds, a part sinks into the soil t> 

 be slowly evaporated, and a very large part is carried 

 away by vegetation itself. Plants drink water and trans- 



36 



