All sewer use charges are due and payable as part of a combined service account under the same terms and conditions as payment for water, as established by the Utility Board of Trustees, but not less often than once every two months. The Clerk may elect to place large volume commercial and industrial users on a monthly billing period. Debt service and user charges shall be shown and separately identified on the regular City bill for potable water, and shall be payable with the water bill at the office of the Clerk.