Any city acquiring, constructing, reconstructing, improving, bettering or extending any works pursuant to this act, shall manage such works in the most efficient manner consistent with sound economy and public advantage, to the end that the services of such works shall be furnished at the lowest possible cost. No city shall operate any works primarily as a source of revenue to the city, but shall operate all such works for the use and benefit of those served by such works and for the promotion of the welfare and for the improvement of the health, safety, comfort and convenience of the inhabitants of the city.