192 
IOWA ACADEMY OF SCIENCE You XXVII, 1920 
the sea, amounts to a great deal and must contribute very largely 
to the eleven or twelve inches of run-off which the upper Missis- 
sippi valley furnishes to the great master stream. 
Conservation of the Ground Water . — How then may we prop- 
erly conserve our stores of underground water? Obviously the 
problem resolves itself into making the most efficient and at the 
same time the most economical use of the supplies with which 
Nature has so beneficently endowed us. Not to use them is to 
waste them. To fail in making them serve to the utmost in the 
advancement of all material and social welfare is as much crim- 
inal negligence as is their wilful or careless dissipation. Hence the 
question is not, Shall we use them? but rather. What is the best 
method of utilization? There are two chief lines along which their 
utilization will proceed, namely domestic and industrial uses and 
agricultural uses. 
For the first of these classes, domestic and industrial uses, 
the quality of serviceable water is rather severely limited. The 
amount of water held in solution, either of solid or of gaseous 
matter, must be relatively small in order not to interfere seriously 
with its palatability, its effect on the human body, its action in 
steam boilers and other industrial machinery. These limitations 
have prevented the use of many supplies which were abundant in 
quantity and easily accessible, at the same time necessitating 
greater drafts upon less abundant but more desirable supplies. 
Thus here the problem is the complex one of securing water that 
is abundant, is easily put where it is needed and is of the proper 
quality. 
Living plants are less fastidious in their demands than are 
mere mechanical plants. Provide them with almost any kind 
of water and they will take from it what they need and reject 
what is useless for their growth. Here the problem is largely 
that of keeping a supply of water within capillary reach of the 
roots. Of course these statements cover only ordinary ground 
water, not acid waters from mines, or industrial wastes and sim- 
ilar classes. 
The Effect of Population Increase . — The rapid growth of popu- 
lation in the upper Mississippi valley, as elsewhere in the United 
States, has made necessary increasingly heavy drafts upon the 
water supply. So long as the population was largely rural or in 
small towns the supply of water needed was drawn from the 
streams or from shallow wells. Furthermore there was relatively 
little pollution of these sources. With the centralization of 
