MICHIGAN ACADEMY OF SCIENCE. 
133 
paratively high degree of chemical purity. If however, the soil and 
subsoil contain limestone or other easily soluble rock debris, as is the 
ease generally in the moraine covered portions of Michigan for example, 
the water after percolating through it, is apt to be too highly charged 
with material in solution to be thoroughly wholesome. 
Deep Wells: The deeper a well is sunk in the earth the less the 
chances of the water supplied by it becoming contaminated with living 
organisms, but the greater the opportunity for it to disolve mineral 
matter. These propositions are based of course, on the assumption 
that water enters the well at or near its bottom. 
Deep wells and springs rising from a deep source, furnish practically 
the only source of water supply for cities which are free from danger 
of contamination by living organisms. It being understood in this 
connection that proper care has been exercised in reference to the in¬ 
troduction of organisms into the well during the process of drilling, 
as on well points for example, and that the water is properly cared 
for after it reaches the surface. When these precautions are taken, 
the water of deep wells furnishes the best of all supplies for city use, 
providing the percent of mineral matter in solution is within certain 
limits in reference to its nature and quantity. 
Having obtained an adequate supply of water from a deep source 
for municipal purposes, however, it is essential that its freedom from 
organic contamination should be maintained. In this connection a 
note of warning needs to be sounded, since in many instances, germ- 
free water is stored in open reservoirs before reaching the consumer, 
and thus exposed to the danger of becoming contaminated from the 
air. This source of danger is especially marked in the case of the 
class of waters under consideration, since the absence or scarcity of 
life in them, including forms not deleterious to the health of man, but 
which as is stated by bacteriologists, are in certain instances the 
enemies of dangerous species, or at least enter into competition with 
them, permits of the rapid development of noxious forms in case they 
do gain admission. 
When water from deep wells or pure springs is utilized by muni¬ 
cipalities, the conditions under which it existed before coming to the 
surface, needs to be maintained so far as possible. If the water is 
stored in reservoirs, such receptacle should be roofed, and during the 
passage of the water through water pipes, etc., man holes and other 
similar openings should be tightly closed. Objections arise, however, 
in reference to the use of covered reservoirs in addition to the expense 
they involve. In many instances the water delivered by deep wells and 
by springs, is of such chemical composition as to make it desirable to 
thoroughly aerate it. In many instances such waters contain gases 
which it is desirable to allow to escape, or are impregnated with min¬ 
eral matter such as iron oxide and calcium carbonate, which if ex¬ 
posed to the air will in a measure be precipitated. Then too, water 
from a deep source is in general deficient in dissolved air, and as people 
are accustomed to drink thoroughly aerated water, its taste is insipid. 
For these reasons thorough exposure to the air of water derived from 
a deep source is in many instances desirable. 
How to keep water derived from a deep source from becoming con- 
