6 BULLETIN 57, U. S. DEPARTMENT OF AGKICULTUBE. 
The above treatment will, in a large measure, purify surface 
water for household uses other than drinking or cooking: but if this 
water is to be used for drinking or cooking it should first be boiled. 
DISTILLED WATER. 
Sometimes a simple still can be conveniently used on a kitchen 
range to provide distilled water for drinking purposes. Saline (alkali) 
waters are satisfactorily treated in this way. Figure 4 illustrates a 
form of still which has been found effective and convenient for house- 
hold use. 1 It has the advantage of being inexpensive and can be made 
by any tinner. The still consists essentially of a water boiler (A) on 
the range, having a capacity of about H to 2 gallons, and a condenser 
suspended at the proper height from the ceiling. The pipe (B) con- 
veys steam to the condensing chamber (C) and is kept cool by water 
in the compartment (Z>). The distilled water collects in (E) and can 
be drawn off from time to time or allowed to run continuously into the 
bucket (F). The metal used in the construction of the still should 
be well-tinned copper and no solder should be exposed to the action 
of either the steam or the distilled water. 
UNDERGROUND WATER SUPPLIES. 
CONTAMINATION . 
It is usual to distinguish between shallow underground supplies and 
deep underground supplies. Wells from 15 to 30 feet in depth to 
water flowing in a layer of gravel or sand, which rests on an impervious 
stratum, are considered as sources of shallow underground supply. 
Both shallow and deep farm wells are often polluted from local 
sources. They are often located for convenience in the barnyard, 
under the barn or stable, close to stock pens, privy vaults, or leaching 
cesspools, or close to the back door, out of which household slops are 
thrown and near which animal and vegetable refuse is often allowed 
to accumulate and decompose. The soil surrounding the well becomes 
saturated with organic filth and, unable finally to perform its useful 
work of filtration and purification, allows the surface water percolating 
through it to carry its load of contamination .into the well. 
The curbing or covering is often loosely constructed of boards, 
permitting small animals and vermin to fall into the well; and 
surface water carrying filth and manure, especially after rams, runs 
into the well from the top. 
The well may be located at such a distance from sources of con- 
tamination that ordinary pumping will bring no bad results, but in 
case of unusually heavy pumping the underground water surface for 
a distance around the well may be sufficiently lowered to reach the 
zone of contamination. This principle is illustrated in figure o. 
1 Montana Sta. Circ. 7. 
