IRRIGATION IN HUMID CLIMATES 417 



likely to take up disease germs. Every open water channel, 

 especially in settled sections, contains to some degree the 

 substances of ordinary sewage, yet none hesitate to 

 use such water for irrigation purposes. The matter could 

 well be subjected to experimental inquiry, before extensive 

 sewage irrigation is undertaken. 



It is ordinarily quite difficult to make the best use of 

 sewage water, because the outlets of sewage systems are 

 usually in low places, and the main problem is that of 

 lifting water to fields. However, in many places it is pos- 

 sible to take out the river water some distance below the 

 outlet of the system and there to apply it to fields. In 

 other places, the sewage might be run into reservoirs and 

 then be pumped to the fields. 



250. Factory and mill waste. While, in general, sew- 

 age waters are admirably adapted to the production of 

 vegetable matter, yet it must not be forgotten that 

 certain kinds of waste are detrimental to plant growth. 

 For instance, the sewage or waste from certain factories 

 and mills is injurious. In the West, it has been found fre- 

 quently that waters coming from gold and silver mills 

 contain poisonous elements. Copper mills have likewise 

 been shown to contaminate water to such a degree that 

 its irrigation value is greatly reduced. Attention should 

 be given, even in the open country, to the possible con- 

 tamination of water by substances which are injurious to 

 plants and animals. 



REFERENCES 



BOWIE, AUG. J., Jr. Irrigation in the North Atlantic States. United 

 States Department of Agriculture, Office of Experiment Sta- 

 tions, Bulletin No. 167 (1906) 



KING, F. H. Irrigation in Humid Climates. United States Depart- 

 ment of Agriculture, Farmers' Bulletin No. 46 (1896). 

 AA 



