If the Utility or its contractor is to install the
water mains, the developer shall be required to advance to the Utility,
prior to the beginning of the construction, the total estimated cost
of the extension. If the final costs exceed estimated costs, an additional
billing will be made for the balance of the cost due. This balance
is to be paid within 30 days. If final costs are less than estimated,
a refund of the overpayment will be made by the Water Utility.