134 
EIGHTH REPORT. 
taminated with objectionable forms of life, and at (lie same time secure 
the desired amount of aeration, is a somewhat difficult problem. The 
details in this connection must of necessity be studied for each special 
locality, but in general it is safe to say that such water should be 
to fall in a spray within n roofed reservoir to which only filtered air 
is admitted and light excluded. Such a provision carries with it also, 
a lowering of the percentage of loss on account of evaporation, and 
prevents a reservoir from becoming a breeding place for mosquitoes, as 
well as eliminating the danger of its becoming foul on account of 
the growth and decay of algae. 
Streams and Lakes: Lakes are in general expansions of streams, but 
in some instances and particularly in Michigan, they originate in other 
ways and are without surface outlets. Examples of enclosed lakes are 
abundant in many regions where the surface of the land is composed 
of glacial drift, and occupy depressions which extend below the water 
table. Water enters them wholly or in part by percolation through the 
material forming the bordering land and their surface levels are de¬ 
pendent on the horizon of the water table. For this reason they are 
similar to shallow wells and are exposed to similar danger of con¬ 
tamination. 
When streams or small lakes are utilized for municipal water sup¬ 
plies, two general plans for striving to insure freedom from organic 
contamination present themselves for consideration: one is to endeavor 
to prevent contamination of the supply and the other to guard against 
such contamination by filtering or by boiling the water. The most log¬ 
ical method is obviously to take advantage of both of these means. 
The sources of supply should be safeguarded so far as possible, and the 
water suitably filtered or boiled before being used for domestic pur¬ 
poses. The boiling of water is as it seems impracticable so far as the 
municipal care of the supply is concerned, and must be left to the in¬ 
dividual. 
If (he region tributary to a surface water supply can be maintained 
in its primitive or natural condition, and men and domestic animals 
excluded, the water derived from it may under normal conditions be 
adjudged reasonably safe and filtration dispensed with. In a region 
which is inhabited and. to a greater or less extent utilized for agricul¬ 
tural purposes, however, it is seldom possible lo insure such a degree of 
freedom from danger of organic contamination, that the surface water 
supplied by it can be safely used for municipal purposes without filtra¬ 
tion. 
In the case of lakes or streams which are utilized for navigation, a 
special (dement of danger is introduced which demands serious con¬ 
sideration in case the water from such sources is used for domestic 
purposes. The-passage of vessels over a water body as the Great Lakes 
for example, leads to the direct introduction into them of refuse of 
many kinds, including the most noxious of all, namely human excre¬ 
ment. In this connection it should be noted that vessels carry people 
from city to city, and that cities are centers of distribution for many 
diseases. This imminent source of danger does not seem to have been 
duly considered in the case of several of the cities of Michigan which 
derive their water supply from the Great Lakes. 
