Said rates or charges for service shall be payable monthly. The owner of the premises, the occupant thereof, and the user of the service shall be jointly and severally liable to pay for the service to such premises and the service is furnished to the premises by the City only upon the condition that the owner of the premises, occupant, and the user of the services are jointly and severally liable therefor to the City. All sewer bills are due and payable 18 days after the billing date. A late fee may be assessed to any bill not paid by the 18th day after the billing date. A late charge of ten percent (10%) shall be charged as provided by the rules and regulations of the Water Department for bills not paid by the 18th day.