Mechanics of the Household / A Course of Study Devoted to Domestic Machinery and Household Mechanical Appliances

by E. S. Keene

RAIN-WATER CISTERNS

Cisterns for the storage of rain water have been used from the time immemorial and are constructed in a great variety of forms. For household use they are often made in the form of wooden or metal tanks, either elevated or placed in the basement; the greater number, however, are of the underground variety made of brick or concrete.

Wooden cisterns are made by manufacturers in different sizes and shipped to the user “knocked down;” that is, they are taken apart and the staves, bottom and hoops are shipped, packed in small space to save space in transportation. Under some conditions they give good service but are apt to leak at times and require attention on that account. In damp basements they give out the disagreeable odor of damp wood.

Tanks made of galvanized iron are much used as cisterns for temporary use. They are inexpensive and give good service but are short-lived. Possibility of leakage is their greatest disadvantage. Underground cisterns are built either in the basement or outside the house. They are quite generally made jug-shaped, but are often constructed of concrete in square and rectangular form. When built of brick the walls are often made of a single course, but walls made of two courses of brick are considered better practice. The walls and floor are made water-tight by plastering with an inch or more of cement mortar.

When cisterns are made of concrete, the floor should be put in 6 inches in depth and as soon after as possible the walls are put up. In good construction the walls are 8 inches in thickness of concrete, made of 1 part good Portland cement, 2 parts clean sand and 4 parts crushed stone. If the cistern is square or rectangular in form the walls should be reinforced with woven wire or steel rods, to prevent cracking.

The curb of the cistern should extend above the surface of the ground sufficiently to prevent surface water from entering, and the top should be covered with a wood-lined sheet-metal cover to prevent freezing.

Filters.

—Unfiltered cistern water is not, as a rule, fit for drinking purposes because of pollution from dust and impurities washed from the roof, but for bathing and laundry work filtered rain water is greatly to be desired.

As rain water comes from the roofs of buildings, there is washed into the cistern a considerable quantity of dust, leaves, bird droppings and other polluting materials which contaminate and discolor the water. This foreign matter is not injurious for the purposes intended, but to render the water clear it should be filtered before using.

Filters for cisterns are quite generally made of soft brick laid in cement mortar, the face of the brick being left uncovered. Fig. 137 illustrates a simple and efficient form of filter made of a single course of brick. A space one-fourth to one-third of the volume of the cistern is left for the filtered water. The opening at the top of the wall must be large enough to admit a man, for some sediment will collect even in the filtered water and the filter must be occasionally cleaned.

Fig. 137.—Cross-section of a brick curbed cistern with a brick filter wall.

Fig. 138.—Cross-section of a concrete cistern with a brick dome filter.

The filter shown in Fig. 138 is dome-shaped and built of brick. The water is pumped from inside the filter and the suction of pumping filters the water as it is used. In this case the filtering action is accelerated by reason of the reduced pressure inside the filter as the water is pumped. The chief disadvantage in this form of filter is the small area exposed for the filtering action and the relatively greater amount of work required for pumping the water, due to the partial vacuum formed as the water is pumped.

The cistern in Fig. 139 is provided with a catch basin which acts as a strainer for removing leaves, etc., that would stain the water. It is made in the form of a concrete basin and partly filled with gravel. The filter in this case is formed by a depression in the cistern floor. A section of tile is placed on the floor, and around it is filled the filtering material of gravel and sand. Filters of this kind are often filled with charcoal or other materials that are expected to purify the water. They are usually inefficient because their value as absorbers of polluting agents is short-lived and unless the materials are frequently renewed they are valueless and sometimes a detriment to rapid filtration.

Fig. 139.—Cross-section of a concrete cistern, containing a sand filter.