Estimating Actual Water Savings: A Different Approach

摘要

In 2007, Dallas launched a toilet replacement and rebate program, called New Throne for Your Home. The program offers a financial incentive to home and multi-family building owners to replace old toilets which use 3.5 gallons per flush (gpf) or more with modern, lowflow toilets that use less than 1.6 gpf. Since its inception, over 21,000 toilets have been replaced. In an effort to determine the true water savings and cost-benefits derived from the New Throne program, statistical models were used to evaluate the program’s effectiveness. Traditional water savings estimates derived from engineering end-use studies heavily reliant on the technical characteristics of devices or programs have often proven to be inaccurate. As a result, Dallas used multiple linear regression models (MLR) to approximate actual water savings, while accounting for the factors of weather, seasonality and customer characteristics. The New Throne program was used to demonstrate the application. Over 2,200 New Throne program participants were selected for this study. Customer characteristics, seasonality, and weather effects were taken into account regarding both indoor and outdoor water use. An average of 1.66 high water use toilets were replaced per family. Our results indicate that each household reduced their monthly water usage by 982.5 gallons. This amount is 46.9% greater than engineering end-use study estimates of 669 gallons. In this case, the use of MLR models in lieu of engineering end-use studies signal the likelihood that greater water savings were actually achieved.