Each joint agency shall, following the closing of each fiscal year, submit an annual report of its activities for the preceding year to each member. Each report shall set forth a complete operating and financial statement covering the operations of the joint agency during the year. The joint agency shall cause an audit of its books of record and accounts to be made at least once in each year by a certified public accountant and the cost may be treated as a part of the cost of construction of a project or otherwise as part of the expense of administration of a project covered by such audit.