Residential Gallons per Capita Day (RGPCD) and Unaccounted-for Water (UAW)
The table below lists the 2006 through 2010 residential gallons per capita day (RGPCD) and unaccounted-for water (UAW) values for Massachusetts Public Water Suppliers (PWSs). RGPCD and UAW are performance standards used to measure how efficiently municipal PWSs are operating their systems. Under the authority of the Water Management Act, municipal PWSs using on average 100,000 gallons/day or more over a year are required to calculate the RGPCD and UAW values for their systems in the Annual Statistical Report (ASR) submitted to MassDEP.
RGPCD is the number of gallons of water used, on average, each day by a resident for purposes such as washing clothes, flushing toilets, showering and lawn watering. RGPCD is computed for a public water supply system by dividing the total metered residential use by the number of residents served by that system. Higher RGPCD values may indicate that residents of the system use substantial water for outdoor use, notably lawn watering. Lower RGPCD values may indicate that a community controls outdoor water use or that the community is densely settled with small lawn areas (for example, cities).
UAW is a measure of how well a water supply system can account for all the water that it pumps into its distribution system. It is the percent of water entering the distribution system not accounted for from service meter readings or from unmetered municipal uses such as fire fighting and street cleaning. UAW values may be high because water is lost through leaks in the distribution system, which may occur in older systems. UAW values may also be high if meters are incorrectly calibrated so that over-registration of water use occurs or if unmetered uses are not documented in the ASR.
For many systems, MassDEP accepted the RGPCD or UAW values reported by water suppliers in their ASR. However, for other systems MassDEP adjusted the values due to calculation errors, wrong methodology used, or insufficient documentation. MassDEP re-calculated populations served by systems that do not serve entire municipalities, adjusting the RGPCD values for these systems if appropriate.
The most common reason MassDEP adjusted the UAW values upward is that water suppliers did not provide sufficient documentation of unmetered water used for municipal purposes, such as fire fighting, water main flushing, and water main breaks. Many water suppliers counted water lost to leaks as a municipal use. However, MassDEP considers leaks to be UAW, and therefore discounted leaks as a municipal use, resulting in higher UAW values.
If you have any questions about how the RGPCD and UAW values are calculated, or why MassDEP adjusted the values, please call Jen D'Urso at 617-654-6591 or email her at firstname.lastname@example.org.
RGPCD Spreadsheet: MS Excel