Talk of the Town: Water use comparison accurate
Nancy Shelton's recent letter questioned the numbers in my recent Talk of the Town, "SRP Wants to Take Everyone's Water," that compared per capita water consumption in the Prescott area to the Phoenix area.
Let me explain the methodology staff used to derive these eye-opening numbers.
First, Gallons per Capita-Day (GPCD) numbers for individual communities do not account for all water uses within their corporate boundaries. For example, the City of Phoenix reports treated municipal water delivered to its customers. It does not include in those quantities untreated water the Salt River Project (SRP) delivers to residential and commercial landscaping, direct delivery of SRP, Central Arizona Project (CAP) and effluent water to golf courses and other uses, and any agricultural, commercial, or industrial uses within the City of Phoenix that have their own supply, or a supply delivered by another water provider.
This complexity makes it difficult to compare one community's GPCD to another. Staff prepared a GPCD comparison of the entire Phoenix Active Management Area (AMA), not just the City of Phoenix, to the entire Prescott AMA.
In the Arizona Department of Water Resources (ADWR) Third Management Plan, the water supply available to Phoenix is more than 2.3 million acre-feet per year, or 2,053,307,671 gallons per day. The Arizona Department of Commerce says the 2008 population of Maricopa County, (which is roughly coincidental with the Phoenix AMA, excluding Wickenburg), was 3,981,500 people (not including Wickenburg). This equates to 515 GPCD.
Using the same sources for the Prescott AMA, the water supply for the Prescott AMA is 21,000 af/yr. To be very conservative, we increased this value 25,000 acre-feet per year, or 22,318,516 gallons per day. We chose a reasonably low estimate of 125,000 people (a higher population estimate would decrease the GPCD value). This equates to 178 GPCD, rounded up to 180.
No method is perfect, but it provides more of an "apples-to-apples" comparison than Ms. Shelton. She did not contact the Town of Prescott Valley to find out that our GPCD value was 105 in 2008, a significantly smaller water use than that quoted for the City of Phoenix. Any reasonable methodology comparing water use and population always will show the Phoenix area is vastly richer in water resources and has a much greater per-capita water consumption than the Prescott area.
(Harvey Skoog is the mayor of the Town of Prescott Valley.)