Effect of Commodity Charges on the Demand for Reclaimed Water

Abstract

Residential irrigation with reclaimed water is one method to reduce potable water withdrawals in the United States. However, little research has examined how customers use this often low cost or free water. This study evaluates the change in water use for 510 reclaimed customers that were converted from a flat-rate to a commodity charge. Using actual water use data and an irrigation model, two metrics of efficiency were developed: portion of landscape needs satisfied and efficiency of application. After the commodity charge began, the reclaimed customers decreased their use by 47% and improved the efficiency of their application by 12%. However, annually between 14 and 27% of the users increased use compared to the flat-rate period. The impact of irrigable area was also evaluated and showed that customers with smaller irrigable areas were less efficient (26%) than irrigators with larger irrigable areas (52%). the reclaimed water demand-supply relationship changes. This study builds on the results of Knight et al. (2015) and presents an analysis of the impact on residential irrigation average and peak monthly demand resulting from a 2008 change in the commodity charge from $0.00 per 1,000 gallons (kgal) to $0.60-0.65/kgal for reclaimed water. The data set for this study is comprised of 510 newer single family residences in Gainesville Florida that were metered at the parcel-level both before and after the implementation of the commodity charge. Using observed changes in monthly water use and a daily benchmark irrigation demand estimation model, the customers' reactions are characterized. By defining the irrigation need, the customer reaction can be defined in terms of their monthly irrigation application. To compare customers and generalize the customer response, a normalization method is presented to classify irrigators based on their water demand. Finally, the results, and their implications, including changes in utility revenue and water supply as a result of changes in customer behavior, are discussed. LITERATURE REVIEW Standard water budgeting calculates the agronomic irrigation demand (AID) as a function of monthly precipitation and evapotranspiration with adjustments for irrigation efficiency and influent water quality (Asano et al. 2007). This approach assumes that demand for irrigation water is independent of price and that irrigators adjust their application rates to coincide with the monthly values of evapotranspiration and precipitation and thereby follow the AID. With regard to the effect of pricing, extensive research has addressed this question. The first Manual of Practice from the American Water Works Association, M1, released in 1954, and now in its 6 th edition, is focused entirely on rate-setting for water providers. Dozens of studies have analyzed the impacts of increasing prices on water demand, e.g., Dalhuisen et al. 2003. In virtually all cases, urban indoor and outdoor demands decreased as price increased.