72 BULLETIN 414, U. S. DEPARTMENT OF AGRICULTURE. 
scrupulously clean and free from filth of all kinds; (3) by constructing 
the well itself in such manner as to prevent the entrance of polluting 
matter. 
CONSTRUCTION OF WELLS. 
A shallow dug well under ordinary conditions should be lined with 
some impervious material, such as concrete, brick or stone laid in 
cement and pointed on the inside, or terra cotta sewer pipe cemented 
at the joints; and this casing should be built as deep into the well as 
practicable. In temporary camps, those in charge usually feel that 
they can afford neither the time nor the material to construct casings 
of any of the materials mentioned above, and rather favor the use of 
wooden casings, used more for the purpose of preventing the sides 
from caving than for keeping out surface pollution. In such cases, 
all precautions as to the location of the well in relation to privies, 
stables, and other sources of pollution become more vital than ever. 
The space between the wooden casing and the earth should be very 
carefully filled with sand or earth tamped as the casing is put in. 
Sand is preferable because it is of value in aiding in the purification of 
any surface water which may percolate through it ; clay is somewhat 
unsafe for the purpose, as some kinds of clay shrink and crack on 
drying, and if this occurs, polluted water may find its way through the 
cracks to the well. Wooden casings, however, should be used only in 
temporary camps, if at all. When used for long periods they decay 
and impart an unpleasant taste to the water, and in the end may be 
more expensive than one of the more durable kinds of casing. 
Driven wells are constructed by attaching a perforated point 
to the end of a pipe from 1J to 4 inches in diameter, and driving the 
pipe into the ground until water is reached. The water enters the 
pipe through the perforations in the point, which are small enough to 
keep out sand and gravel. 
The upper end of the pipe usually is attached directly to a pump 
by which the water is raised. The vibration of the pipe, caused by the 
pump, often loosens the earth about the tubing so that a channel is 
formed through which surface water may enter the well; and the 
joints in the pipe also have been known to loosen so as to permit the 
entrance of surface water. To obviate the former trouble it is neces- 
sary to provide a heavy timber or concrete platform to which the 
frame of the pump may be fastened tightly. The pipe should be 
inspected occasionally with a view to the removal of all leaky and 
rusted sections. Waste water from the pump should be carried by a 
pipe or spout to a considerable distance from the well, and dirty 
water never should be used in priming. 
When a distance of 100 feet or more is traversed before water 
is struck, the 'term " deep well" is commonly applied. If, after water 
