In order that the residential users discharging sanitary sewage not be penalized for sprinkling lawns, washing cars, watering gardens, etc., during the months May, June, July, August, September and October, the billing for sanitary sewer services for residential users for the months of May, June, July, August, September and October (summer average) of a particular year shall be based upon that user’s average monthly water usage billed during the months January, February, March, April, November and December (winter average). Residential sanitary sewer services applicable to the Summer Average shall apply to each lot, parcel of real estate, or building which is occupied and used as a residence. The Summer Average shall not apply to any premises which are partially used for commercial or industrial purposes. The Winter Average shall be determined by the customer’s actual usage using the previous months November thru April. When the average is calculated, the high and low readings will be discarded. If a customer has less than six (6) readings, the number shall be defaulted to a value of eight hundred (800) cubic feet. For billing purposes, a minimum of three (300) hundred cubic feet shall be set and the lesser of the actual/average (default if used) will be charged.