THE PURITY OF DRINKING-WATERS I41I 
all streams upon whose banks are human habitations are polluted 
and unsafe for drinking. The question of the purification of such 
water will be noticed later. 
Wells.—Next to running streams, wells are the most dangerous 
source of drinking-water. The extent of the danger depends upon 
the location of a well and its depth. In very deep wells bacteria 
have a chance to be filtered out of the water as it passes through the 
soil before it reaches the well; so that, if care be taken to prevent 
contamination at the surface, the water is safe. This is always 
true of artesian wells. But in the shallow well the chance of dan- 
gerous contamination is great. The most common, as well as the 
most dangerous contamination of well-water, comes from the privy 
vault. Both vault and well are, for convenience, placed near the 
house and frequently near each other. The well is sunken several 
feet below the surface of the ground, while the vault is close to the 
surface. The contents of the vault inevitably soak into the ground 
and will be surely distributed in every direction, taking naturally 
the course of water currents under the surface. It is almost cer- 
tain that, if the well is close at hand, the water courses will lead 
to it and the contents of the vault will thus find their way into the 
well. It requires no argument to demonstrate the danger from 
such conditions. Nor will anyone familiar with agricultural 
communities fail to recognize that exactly such conditions fre- 
quently exist. Indeed, they are sometimes even worse than this, 
for one may find the vault actually upon an elevated mound and 
the well sunk into the soil at its foot not twenty feet away. 
Under such conditions one need not be surprised at the spread 
of typhoid. A single case of the disease on the farm will con- 
taminate the vault, and may soon infect the well. The infection 
may be from water percolating through the soil or from surface 
currents in time of rains, washing the contaminated water into 
the mouth of the well. The farmer rinses his milk pails in the 
water from the well and subsequently puts his warm milk in the 
cans. The typhoid bacilli which were in the well thus get into 
