In most cities to-day the pollution of streams is prohibited on two grounds, first, that the streams are public property, even though for a part of their course they may be owned individually. The sum of the parts making up the whole stream involves so many individuals as to imply public ownership, and inasmuch as one individual is limited in his uses of the stream by the principle already referred to, he cannot, even on his own land, do what he pleases with a stream or with its waters. When streams are navigable, according to the law of this country, no private ownership can exist, for the waters are controlled and owned by the federal government. This latter body, in general, does not undertake to control the quality of such waters, but there are many laws covering the quantity of water in such streams, limiting the amounts that can be withdrawn, restricting the filling up or silting of such streams, and qualifying the bridging or damming of such waterways. In small streams, such as are generally found in rural communities, the vital principle of ownership is always limited by the requirement that no owner shall so interfere with the normal quantity or quality of water in the stream as to prevent their full enjoyment by the next man downstream whose rights are equal with his own. This means, in the matter of quantity, that while one individual may water stock in a stream or may pump water from a stream for household use, he may not withdraw from the stream the entire volume to use for irrigation, nor may he, as a riparian owner, sell the water to some city near by which might take out all the water of the stream. The quality of a stream, likewise, may only to a certain extent be interfered with. If a stream flows through a meadow, cows pastured in the meadow have a natural right to wade in the brook, and if, in so doing, a certain amount of pollution is added to the waters of the brook, no one downstream can justly complain. If, however, a sewer is carried from barns or houses into a brook which is later used for drinking purposes, the quality of the water is affected, and such a discharge is so revolting to the senses that complaint to the courts would result in an order to find some other method of disposing of such wastes.