A district may provide for a reserve fund to be used for the payment of the interest or principal of any outstanding bonds. If the estimate referred to in Section 24955 and the order determining the amount of bonds provided for in Section 24962, provide for a revenue bond reserve fund in a specified amount to be set aside out of the proceeds of sale of revenue bonds, then the district may, upon the sale of any bonds payable solely from revenues, create such revenue bond reserve fund and set aside in such fund out of the proceeds of sale of such bonds a sum not exceeding such specified amount, such fund to be maintained from revenues and used and withdrawn solely for the purpose of paying the principal of and interest on such bonds in the event that no other funds are available therefor.