A: Yes. Sewer charges are based upon the average amount of water a household consumes during the winter months (November, December and January), when water consumption is generally the lowest. Sewer charges are recalculated once a year in the spring, this applies to Residential Accounts only. The City of Southlake is one of the few cities that offers sewer averaging as well as capping the sewer charge for 10,000 gallons used.