Cisterns are vessels employed for the reception of rain, or water, either under ground, such as those of navigable carials, etc. or above ground, for domestic and other purposes. In this place, we shall treat only of the latter.

As the water collected in leaden cisterns is apt to corrupt, either by stagnating tor several days, when the pipes happen to be, obstructed, or by the deposition of feculent matter, as well as the incrustation formed in such vessels, it follows that they ought to be frequently cleansed of the copious sediment they contain. This attention is the more necessary, as lead is a metal liable to be dissolved by and, in that state, proves a slow, but fatal poison. Although' the acidity contained in stagnant water which has, in its course, been impregnated with animal. vegetable particles, cannot be very considerable, yet it will be more and prudent, to prevent the formation of such acids, by an early attention to the purity of the water. See FILTRATION.