BACTERIA IN WATER. 163 



CHAPTER VII. 

 BACTERIA IN WATER. 



WHILE not very closely related to agricultural problems the 

 subject of bacteria in water has certain aspects, particularly 

 relating to water as a distributor of disease, which are of especial 

 interest to the farmer who must control his own water supply. 

 We will therefore consider the matter here, although it can be 



o 



done quite briefly. 



ABUNDANCE OF BACTERIA IN WATER. 



All surface waters abound in bacteria. If we examine the 

 water of the ocean, or of the pool by the roadside, we shall 

 always find bacteria in greater or less numbers. Waters com- 

 ing from far below the surface of the earth appear to be sterile. 

 Thus water coming from artesian wells contains few bacteria, 

 provided it can be drawn in such a way as to prevent contami- 

 nation before it reaches the surface. From this it follows that 

 spring water is also quite likely to be pure, at least purer than 

 other surface waters, although it will rarely be sterile, since 

 there is always a chance for contamination in the superficial 

 layers of the soil. Rain water always contains bacteria which 

 are doubtless washed out of the air ; and the same is true of 

 snow and hail. 



The number of bacteria in bodies of surface water is not 

 exactly what would be expected in accordance with our ideas 

 of pure water. We commonly look upon the water in the 

 running brook as purer than that of the stagnant pond, and 

 might be inclined to believe the brook freer from bacteria. 

 But this is certainly not true, for the brook commonly contains 



