For the purpose of determining the amount of taxes which may be raised on real estate pursuant to section ten of this article, the revenues received in each fiscal year by any county, city or village from a public improvement or part thereof, or service, owned or rendered by such county, city or village for which bonds or capital notes are issued after January first, nineteen hundred fifty, shall be applied first to the payment of all costs of operation, maintenance and repairs thereof, and then to the payment of the amounts required in such fiscal year to pay the interest on and the amortization of, or payment of, indebtedness contracted for such public improvement or part thereof, or service. The provisions of this section shall not prohibit the use of excess revenues for any lawful county, city or village purpose. The provisions of this section shall not be applicable to a public improvement or part thereof constructed to provide for the supply of water.