8 BULLETIN 495, U. S. DEPARTMENT OF AGRICULTURE. 
nections being commonly used. Only removable suction pipe should 
be placed in surface supplies which freeze in winter. 
STORAGE WATER. 
In many cases excellent water supplies for spray irrigation plants 
are obtained from streams, drains, and wells which do not have a ~ 
continuous flow of water sufficient without storage. In such cases 
the water may be stored in a small reservoir. Figure 1 illustrates a 
small stream across which an earthern dam has been built at a point 
where it will back considerable water over a flat area and hold it 
until the farmer needs to irrigate. In the Eastern States much 
smaller reservoirs can be used than in the arid regions, because the 
rains are more frequent and are sufficient to make the small streams 
flow every few weeks. Likewise in the more humid sections water 
from farm drains and rain water flowing from hillsides and roofs 
of buildings can be conserved by storage in reservoirs or cisterns 
built of clay brick or cement, and in this way many gardens may be 
saved in dry periods. A section in eastern Pennsylvania is rep- 
resentative of the Eastern States where spray irrigation has devel- 
oped. The writer estimates from a study of rainfall records and 
drought periods covering 20 growing seasons in this section that 
the storage of the water falling on the roof of a building during the 
summer months is sufficient to irrigate a garden which is three times 
the area of the building. The reservoir in this case would need to 
hold about two months’ rainfall or the equivalent of 6 inches falling 
on the roof. 7 
UNDERGROUND WATERS. 
Underground waters may be divided into ground and artesian. 
To the first belong the waters which are nearest the surface and more 
or less influenced by local rainfall, seepage. and droughts. The 
waters of the second group are confined under pressure beneath an 
impervious stratum, usually located at considerable depth below the 
surface. Such water, when tapped by boring, will rise in the well 
and sometimes overflow at the surface. The development of under- 
ground waters is usually more expensive than obtaining a supply 
from surface sources. However, when a farmer is able to obtain — 
undereround water at a reasonable depth near or in the center of the 
field to be irrigated the saving in cost of piping may largely offset 
the expense of sinking wells. . 

1 Various types of small reserveirs which would be of value to readers of this bulietin 
are discussed in Bulletin No. 179, of the Office of Experiment Stations, and part 1 of 
Office of Experiment Stations Bulletin No. 249. The department’s supply of these bulle-_ 
tins has been exhausted, but copies can be obtained from the Superintendent of Docu- — 
ments, Washington, D. C., at a cost of 20 cents each. 


