6 
bulletin 83. 
Upon its entering the plains it begins to receive an increased 
amount of mineral matter and we soon find from four to more 
than seventy times as much and the water passes from a soft, 
mountain water to a hard, alkali, plains water. This change can 
be detected within a short distance of the point where the streams 
leave the mountains' 
The water then that we use for irrigation rarely has the 
same purity that it possessed in the mountains. In one ex¬ 
periment I found that in flowing about ten miles through a ditch, 
the mineral matter carried by the water increased fivefold. This 
mineral matter came, of course, from the land adjacent to the 
ditch. 
In onr natural waters, those of our mountains, it is proper 
and in perfect accord with what we would expect, that they 
should contain corbonate of lime, magnesia, etc. and we find such 
to be the fact, but as soon as they pass into the plains section of the 
stream they begin to exchange these for the sulfates until these 
latter become the predominating salts. In the meantime the 
three grains per gallon in the mountain water have become 100 
grains per gallon in the plains water. This is not an exaggerated 
statement, but one far within the limits of fact. The water of the 
Cache la Poudre carries in the mountain sections of its course 2.9 
grains of mineral matter per gallon, and just above Greeley, 115 
grains, the carbonates constitute nearly 40 per cent of the former 
while magnesia sulfate, Epsom salts, constitute nearly one-third 
of the latter. Almost the same statement can be made of the 
Arkansas, at Canon City, the river water carries say 10 grains per 
gallon, below Rockyford 156 grains. The carbonates constitute 50 
per cent, of the former while Glauber and Epsom salts constitute 
40 per cent, of the latter. 
In neither of these statements have I taken any account of the 
calcic sulfate. It is difficult to judge how much of this change is 
directly attributable to irrigation. Irrigation may exaggerate 
these changes but that they would take place in a large measure 
if there were no irrigation is indicated by the fact that they begin 
immediately, so far as we can see, upon the waters leaving the 
mountains, and also by the changes in the water in ditches above 
which there is but little or no irrigated land. 
The cause of these changes is the entrance of water from the 
land adjacent to the river course, or return waters. 
In order to hold the flood and other waters until they can be 
applied to crops and be made beneficial to the country, large reser¬ 
voirs have been established and the river waters conducted into 
them and retained there for varying periods. These reservoir sites 
are depressions capable of having their holding capacity increased 
by embankments thrown up or built in the proper place. They 
