1893-1894 - The University of North Carolina at Chapel Hill

222 APPENDIX.
AUOKISMUM.
SUGGESTIONS AND INSTRUCTIONS FOR BUILDING CISTERNS
FOR THE STORAGE OF RAIN-WATER.
BY J. C. CHASE, ENGINEER OF THE BOARD.
The most satisfactory form for an underground cistern for storing rainwater
is circular in plan, covered with a dome arch ten or twelve feet in
diameter and of the rec|uired depth to store the desired quantit}-. The
smallest size that is usually constructed
contains one hundred barrels, or
thirtv-one hundred gallons. This quantity would furnish an average
daily supply of fifteen gallons for a period of six months.
It is considered
advisable to have the cistern full by April ist, and have it of sufficient
capacitv to last till the fall rains set in; therefore the size will depend
upon the prospective consumption, whether it is used merely to store
water for drinking and cooking or is expected to furnish a supply for
general uses about the premises, such as washing, watering stock, etc.
In the latter case it would be better to provide two cisterns—one of which
could be used for storage as the rains occurred and the other be reserved
for household use.
The method of construction is shown in the accompanying drawing,
and little additional explanation will be necessary. Care should be taken
that the bottom be built on compact material, also that the earth is
thoroughly packed around the outside of the structure. If built in hard
luaterial, such as stiff, dry clay, it ma}' be practicable to make the excavation
just enough larger to allow for a course of h}'draulic cement mortar
between the brick-work and the earth. The brick may be laid in lime
mortar, but in that case it will be necessary to thoroughly plaster the
structure both outside and in with a good coating of hydraulic cement
mortar. The inside should be well and smoothly plastered in au}- event.
The mortar for plastering should be made of pure cement.
The supply pipe from the roof should have the customary valve (Fig. 3)
for wasting the rain-fall until the roof is thoroughly washed, and also after
the cistern is full. The water should also be filtered through sand and
gravel, from which the loam has been washed out, or charcoal, or a mixture
of all three, before passing into the cistern. The same general
method should be followed in constructing the filter as has been detailed
for the cistern. The filter should be thoroughly cleaned out and the
material washed each year. It is also desirable to clean the cistern, but