(2) Rates so fixed shall be sufficient to accomplish the following purposes:
(a) For proper operation and maintenance of the property or facilities owned by the district.
(b) To pay all taxes which may be levied upon property owned by the district or which it may be required to pay out of its gross revenues.
(c) For payment of principal and interest of all bonds, warrants or obligations of any character in accordance with terms and provisions thereof respecting time, manner and amount of payment.
(d) For payment of any other indebtedness or obligations which the district may be obligated to pay.
(e) To establish and maintain any special funds which the district has obligated itself to create for the purpose of paying bond issues or other obligations.