242 DUST AND WATEE. 



The purity of ground water depends entirely upon 

 where it comes from and upon its environment. Being 

 the water which is held by the impervious stratum of 

 clay or rock immediately below the earth's surface, it 

 may form the source of our purest springs, and it may in 

 certain localities and under certain conditions become 

 dangerously contaminated. It should never be used for 

 drinking, in closely settled communities, or when drawn 

 from wells which have been sunk near cesspools, stables 

 or closets, I think that the liability of ground water 

 wells to contamination, may be illustrated by the effect 

 which the construction of the sewer system of the city of 

 Poughkeepsie had upon them. They were invariably 

 drained, and rendered useless as sources of water supply. 

 Thus the construction of the sewers conferred a benefit 

 upon the city, not originally contemplated. The water 

 of the Fallkill may be classed as surface water, or as 

 ground water which has not been filtered ; and may not 

 be regarded as a strictly pure water, inasmuch as it re- 

 ceives a great deal of questionable drainage during its 

 course. It is however a swiftly flowing stream, and the 

 constant aeration which its water receives, tends strongly 

 to purify it. Its uncertain and inadequate quantity even 

 in rainy seasons, makes it unreliable as a source of gen- 

 eral supply for the city. 



Aetesian Wells. — In the wonderful construction of 

 the earth's crust there are below the depressions and 

 subterranean water courses formed by the upper strata 

 of clay and rock, other and deeper recesses, where 

 flowing streams and lakes of water abound — all more or 

 less pure, according to the environment. 



These are reached by deep wells reaching thousands of 

 feet sometimes and known as artesian wells. They are 

 not always successful in producing pure water, although 

 they are frequently very successful — producing without 

 pumping a large quantity of excellent water. The cost 



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