WaterSense Program: Methodology for National Water Savings Analysis Model Indoor Residential Water Use

The U.S. Environmental Protection Agency (EPA) influences the market for plumbing fixtures and fittings by encouraging consumers to purchase products that carry the WaterSense label, which certifies those products as performing at low flow rates compared to unlabeled fixtures and fittings. As consumers decide to purchase water-efficient products, water consumption will decline nationwide. Decreased water consumption should prolong the operating life of water and wastewater treatment facilities. This report describes the method used to calculate national water savings attributable to EPA?s WaterSense program. A Microsoft Excel spreadsheet model, the National Water Savings (NWS) analysis model, accompanies this methodology report. Version 1.0 of the NWS model evaluates indoor residential water consumption. Two additional documents, a Users? Guide to the spreadsheet model and an Impacts Report, accompany the NWS model and this methodology document. Altogether, these four documents represent Phase One of this project. The Users? Guide leads policy makers through the spreadsheet options available for projecting the water savings that result from various policy scenarios. The Impacts Report shows national water savings that will result from differing degrees of market saturation of high-efficiency water-using products. This detailed methodology report describes the NWS analysis model, which examines the effects of WaterSense by tracking the shipments of products that WaterSense has designated as water-efficient. The model estimates market penetration of products that carry the WaterSense label. Market penetration is calculated for both existing and new construction. The NWS model estimates savings based on an accounting analysis of water-using products and of building stock. Estimates of future national water savings will help policy makers further direct the focus of WaterSense and calculate stakeholder impacts from the program. Calculating the total gallons of water the WaterSense program saves nationwide involves integrating two components, or modules, of the NWS model. Module 1 calculates the baseline national water consumption of typical fixtures, fittings, and appliances prior to the program (as described in Section 2.0 of this report). Module 2 develops trends in efficiency for water-using products both in the business-as-usual case and as a result of the program (Section 3.0). The NWS model combines the two modules to calculate total gallons saved by the WaterSense program (Section 4.0). Figure 1 illustrates the modules and the process involved in modeling for the NWS model analysis. The output of the NWS model provides the base case for each end use, as well as a prediction of total residential indoor water consumption during the next two decades. Based on the calculations described in Section 4.0, we can project a timeline of water savings attributable to the WaterSense program. The savings increase each year as the program results in the installation of greater numbers of efficient products, which come to compose more and more of the product stock in households throughout the United States