Where sewer user fees are calculated in whole or in part by using the volume of water consumed per month, and the user paying such fees does not use water from the water system of the city, said user shall at his expense install a meter in a manner first approved by the director of public works to measure the quantity of the water, or the monthly quantity shall be determined by the director of public works based on calculations and figures provided by the user showing or estimating average monthly consumption of water. (Ord. 79-74 §3, 1979).