For the purpose of protecting the water supply furnished to the inhabitants of the city from pollution, and for the preservation and protection of the purity of the water supply, the city assumes jurisdiction over all the property occupied by the works, reservoirs, systems, springs, branches and pipes by means of tributaries constituting the sources of supply from which the city obtains its supply of water, and over all streams, creeks or tributaries constituting such sources of supply, whether the same or any part thereof are within the corporate limits of the city or outside thereof.