It is hereby expressly provided that contract customers of the City waterworks shall be billed on a monthly, as opposed to a quarterly, basis for their total water consumption. The rates chargeable shall be the same as those chargeable to any other customer of the City provided however, that all amounts of water consumed over and above 500,000 gallons in any given quarter shall be billed at the appropriate rate for water consumed in excess of 500,000 gallons. (10-12-82)