To determine the amount of rain water available from a certain roof, ascertain the amount of surface of its horizontal projection, and multiply this by the annual rainfall in feet and decimals of a foot. The total amount in cubic feet must be divided by two, to allow for unavoidable loss through evaporation and for wasted, impure roof washings. It is easy to arrive at a proper size for the cistern, if the available amount of water is known.
In collecting roof water, it is important to allow the first washings from the roof, which always contain more or less filth in the shape of dust, horse dung from the street, excrements of birds, leaves from trees, etc., to run off on the surface. This may readily be accomplished by cut-offs on the rain water pipes, to be worked by hand or arranged to act automatically. The best roofing surface for collecting rain water is slate, and next to this shingles. Underground cisterns are usually built circular in shape, of hard-burnt brick, laid in hydraulic cement. The walls of the cistern must be made perfectly watertight, not only to prevent leakage from it to the outside, but also to prevent the entrance into it of ground water. If an overflow pipe is provided, it should under no circumstances whatever communicate with any drain or sewer, or discharge into a cesspool. As soon as delivered into the cistern, the water must be kept scrupulously clean, and any possible source of pollution should be removed. It is a good plan to build into the cistern a filtering chamber to remove the coarser impurities in the water. Cisterns should be frequently inspected, emptied and cleaned; the opening at the top must be closed by a solid cover, to prevent the falling in of vermin, mice, rats, etc., and to guard against contamination by surface-washings.
Occasionally a dwelling-house is supplied from a distant spring, by a gravitation supply in case the spring is near a hill-top, or by means of a hydraulic ram if the spring is situated at a lower level than the house.
If the dwelling draws its supply from a well or a cistern, the water is usually lifted by means of suction-pumps, generally located, for convenience’s sake, inside the house, at the kitchen sink. If the cottage has any plumbing fixtures on the upper floor, it becomes necessary to force water by a lift and force-pump to a small reservoir or tank under the roof, from which it is distributed to the fixtures under a constant head of pressure. Such water tanks should be made of cast iron well painted, or of wrought iron well protected against rust. Slate tanks are also very good. Cheaper than either of these are wooden tanks. Wooden tanks are often lined with tinned copper; lead, zinc or galvanized iron linings are undesirable. Care must be taken not to run the overflow of a tank into any soil or drain pipe. The simplest way of disposing of it is to run it into the gutter of the roof. If this is not feasible run it down to the kitchen sink, and make it serve as a tell-tale for use with the force-pump at the kitchen sink.
Pipes for conveying water to the plumbing fixtures may be of drawn lead, or tin-lined lead, or of block tin. Wrought iron is used extensively, either plain or galvanized or enamelled; rubber-coated, glass-lined and tin-lined wrought-iron pipes are also made, but are too expensive for ordinary use.
Drawn lead pipe is a material possessing many merits, and hence it is used extensively. It should be remembered, however, that soft water attacks lead, and a sufficient amount of lead is occasionally dissolved to cause dangerous poisoning of persons drinking water from such pipes. It is a good precaution in the case of new pipes to allow the water to run for a while, especially if it has been standing in the pipes over night. Tin-lined pipes, although more expensive, are much safer for use, but great care must be taken in making joints in such pipe, lest the tin be removed at the joints. Tin-lined as well as block tin pipes should always be used as suction-pipes in wells and cisterns in preference to ordinary lead pipes.
Plain wrought-iron pipes rust quickly, especially if not constantly kept full of water; water conveyed through them is apt to make iron stains in the washing. A further disadvantage is the frequent choking up of the smaller sizes through rust. Pipes coated with some kind of enamel are better and safer, provided care is taken in making the joints properly. Plain wrought-iron pipes, made rustless by the Bower-Barff process, have lately been used and promise to show good results. Wrought-iron pipes are largely used, protected with a coating of zinc, and such “galvanized” pipes may be safely used, for, although water dissolves and is often found to contain salts of zinc, which are poisonous in large amounts, dilution makes them practically harmless. A more serious objection to galvanized pipes may be the fact that the zinc coating, unless applied with great care, soon wears off and ceases to protect the pipe against rust. Copper tubes, lined with tin, are occasionally used, but are expensive and troublesome to put up. In some of the Eastern States drawn seamless brass tubes are used for hot-water pipes. Their only advantage over lead would seem to be their neater appearance and less liability to sag, although changes of temperature affect brass pipes by expansion and contraction, causing leaky joints. Brass pipes, if used for drinking-water, should be tinned on the inside.
It is important to arrange all water-pipes so that they can be completely drained or emptied, when the supply is shut off. Pipes running on outside walls should be suitably protected against frost. It is recommended, even in the case of the smallest buildings, to have a plan, showing the exact size, material and location of all water pipes, stop-cocks, faucets, cisterns, etc. All pipes should be kept accessible, and, wherever possible, in sight.
The supply for drinking purposes is often purified by means of domestic filtration. This is especially desirable with cistern water. Domestic filters should act not only as strainers by removing suspended impurities, but they ought also to act chemically by oxidizing a part or all of the dissolved organic matter. Various materials are used for domestic filters, amongst them being sand, sponge, flannel, cotton, animal charcoal and spongy iron. Nothing is more erroneous than the supposition that a filter, once started, will continue to act, without further attention, forever. Whatever the filtering material may be, it should be frequently cleaned and aerated, and renewed from time to time. It must, therefore, always be easily accessible. Most small filters, to be screwed to faucets on the supply pipe, are made reversible, and if this operation is regularly performed, they work quite well, although their action is of necessity largely mechanical. Larger filters are connected by means of a hose or a pipe with the pressure supply, and these, too, answer well, provided they have an arrangement for periodical reversing of the direction of the filtering current. Other filters are portable vessels to be filled by hand. Filters are also placed in cisterns, or at the end of the suction pipe in wells or cisterns. A good plan is to build into the cistern a partition wall, establishing a small chamber, in which the suction pipe is placed. The dividing wall is built with courses of brick, some of which, being laid dry, act as strainers. This arrangement, it need hardly be said, wants periodical cleaning as much as any of the household filters.