The department is authorized to expend funds appropriated or available to the department for the acquisition, construction, development, extension, enlargement, or improvement of water and sewage treatment facilities or systems to serve planned communities which have been certified as eligible for state development assistance under Code Section 45-12-170. Such funds may come from appropriations of the General Assembly for such purpose, or general obligation bonds may be issued for funds for such purpose. The department may require as a condition of such development assistance that provision be made for the purchase by the appropriate local government of such facilities or improvements for an amount up to the amount of such funds expended by the department plus accrued interest. The department and local governments may also enter into agreements whereby such projects are leased to the appropriate local government, provided that such lease payments, exclusive of payments for operating costs, shall be included in the total amount necessary to purchase such projects.