The funds received from the collection of the service charges authorized by this chapter shall be deposited daily with the Director of Finance and shall be accounted for and be known as the Water Fund and when appropriated by the City Commission, subject to the provisions of any ordinance or indenture of mortgage authorizing issuance of any securing mortgage revenue bonds for the water works system, shall be available for the payment of the costs and expenses of the management, maintenance and repair of the City water system and the water treatment plant, and any surplus in the Fund following such payment shall be used for the payment of the interest on bonds issued and outstanding or which may be issued to provide funds with which to pay the City's portion of the cost of constructing such water system or part thereof and the water treatment works, and to retire such bonds when they mature, and for costs incurred in the enlargement or replacement of the water system and treatment works.