WATER. 
155 
plant and animal matter that is decaying in the 
soil. 
“ The best wells are those that are bored deep 
through the subsoil until water is reached. The 
water from these is always wholesome. 
6. “ Rivers and lakes yield us a supply of very 
good water, if they do not become fouled by decay- 
Artesian Wells. 
The wells at A, B, C tap layers of water at different levels— shown 
by the heavy black lines. 
ing matter. In the upper course of a river the 
water is mostly wholesome and pleasant. But in 
the lower lands, when it has drained over the 
surface of cultivated fields, or received the refuse 
of dwellings and cattle-pens, it is not unlikely that 
illness may be caused by drinking it. The move- 
ment of the running water, however, helps to allow 
the oxygen of the air to purify it. 
7. “ The danger of illness is especially great where 
