Section 14. The commissioners shall at least once a month at such time as the board may require submit to it the accounts and vouchers for expenses incurred in meeting the cost of required improvements under sections one to fourteen B, inclusive. Such accounts and vouchers shall be inspected by the board and if it approves the same it shall forward them to the county treasurer or to the state treasurer, as the case may be, for payment from any funds which may be available for the purpose. Expenses for maintenance or for further improvements incurred under the direction of the prudential committee of the district as provided in section fourteen A shall be paid by the district treasurer on presentation by the prudential committee of accounts and vouchers for such expenses; provided, that accounts and vouchers for expenses incurred in connection with further improvements shall be subject to the approval of the board before payment. The commissioners appointed under section fourteen A to make further improvements shall present their accounts and vouchers to the board for approval in the same manner as the commissioners appointed under section five to make the original improvements.