No. 4.] FARM WATER SUPPLIES. 315 



would be required to collect from the average rainfall the quan- 

 tity of water used by the family. This would mean a circular 

 space of ground 104 feet in diameter; but, inasmuch as a large 

 part of the rainfall runs off of the ground as it falls, the amount 

 that a well is capable of yielding practically never equals the 

 amount of the rainfall. 



An average of one-third of the rainfall on the drainage area of 

 a well is a very large yield, and the quantity is usually much 

 less. Assuming that one-fifth of the rainfall is collectible in a 

 well, the area of ground required for securing a supply of 600 

 gallons daily would be a space 230 feet in diameter; that is, a 

 privy or cesspool located within 115 feet of a well which derives 

 its water equally from all directions would be likely to drain 

 toward it, even if the rainfall were distributed in equal daily 

 quantities throughout the year. 



Of course, the yield of rainfall varies, the amount being large 

 in the winter and spring and small in the summer and autumn, 

 so that in the drier portion of the year water would probably be 

 influenced to flow toward the well from a considerably greater 

 distance than 115 feet. 



The foregoing figures refer only to average conditions where 

 the soil is of the same porosity and character over a consider- 

 able area. As the character of the soil usually varies consider- 

 ably, even in short distances, the flow of ground water is 

 probably not usvuilly the same from all directions about a well. 

 There is also likely to be a variation in the flow of water 

 toward a well due to the slope of the ground water, so that 

 pollutions discharged into the ground may be carried to the well 

 from a much greater distance on the side of the well from which 

 the ground water flows most freely than pollutions deposited in 

 other directions about the well. 



The surest way of securing a supply of water that is safe for 

 drinking from a well dug near a farmhouse is to so locate the 

 well and the places of disposal for sewage, viz., sink drain, 

 cesspool, privy, barn, etc., that drainage from any of these 

 will not affect the well. The best plan is, of course, to locate 

 the sink drain, cesspool, privy and barn at a lower level than , 

 the well, but obviously this can be done only in comparati\'ely 

 few cases where it is desired to locate the well in the immediate 



