All bills rendered water consumers in accordance with the current rate schedule are payable to the city at the City Hall therein on or before the tenth day of the month following the billing.  All bills so rendered and not paid by the date shall bear a delinquency charge in the sum of 10% thereof, which delinquency charge shall, after the tenth day of the month, be payable in addition to the charge made in accordance with the water rate.
(`83 Code, § 17-306)