Cisterns composed of metal throughout embrace old cisterns of cast lead, dated early in the 18th century; these are quite harmless, on account of their natural silver alloy, and they may be trusted, all other conditions being satisfactory. Cast-iron cisterns, made of plates bolted together, if kept full, and not subject to rust, are unobjectionable. Wrought iron, which has afterwards been “galvanised,” is a very common form of cistern, and appears to be the cheapest. Little can be said in its disfavour, although experiments made in America have proved that some waters attack the inner coating. The commonest form of cistern is composed of wooden framing lined inside with sheet lead. This is not the best for storing drinking-water, and slate would be preferable; but no one would say that all water drawn from leaden cisterns would injuriously affect health. The interior of a lead-lined cistern will be found to acquire a whitish coating, and it is due to this chemical alteration of its surface that the contained water can be drunk with more or less impunity. Nevertheless, there are some waters which very readily attack lead, and care should be exercised in this respect. In cleaning out a lead cistern the surface should never be scraped, but simply washed down with a moderately hard brush. Sometimes houses are provided with zinc-lined wooden cisterns; this metal for several reasons is one of the worst materials for water storage, and should never be used for drinking-water. Neither should wooden butts or barrels be employed for storing water anywhere in a house, as they speedily become lined with a low vegetable growth detrimental to health. A great mistake consists in storing away a great quantity of water in abnormally large cisterns, in consequence of which the tap is drawing off for a very long period the water first delivered to it, and which is not the cleanest water. This does not so much matter in cisterns which supply closets or baths, but it is reprehensible when the water is for the bedroom decanter and the nursery.