POWTS are sized based on the number of bedrooms in a structure or proposed structure for residential applications. Commercial sizing will not be discussed. Typically the sizing is based on 75 gallons per person per day with a proposed occupancy of 2 people per bedroom. With this standard in mind, the average 3-bedroom home will have a calculated daily wastewater flow (DWF) of 450 gallons per day.
After determining the DWF the POWTS installer can size the necessary treatment tank(s) properly. After reviewing the soil and site evaluation report, that was performed by the certified soil tester, the installing plumber can then determine the minimum size of absorption field required which is based on the soil load rate that is specified on the report form.