Methodology For National Water Savings Model and Spreadsheet Tool - Outdoor Water Use

This report describes the method Lawrence Berkeley National Laboratory (LBNL) developed to estimate national impacts of the U.S. Environmental Protection Agency's (EPA's) WaterSense labeling program for weather-based irrigation controllers (WBIC). Estimated impacts include the national water savings attributable to the program and the net present value of the lifetime water savings for consumers of irrigation controllers.

LBNL developed a mathematical model to quantify the water and monetary savings attributable to the WaterSense labeling program for outdoor products. The National Water Savings-Outdoor (NWS-O) model is a spreadsheet tool with which the EPA can evaluate the success of its program for encouraging buyers to purchase more water-efficient irrigation products. WaterSense initiated its program for outdoor products by focusing on WBIC. EPA places its WaterSense label on WBIC products that meet a set of technical specifications. WBICs have been shown in a number of field studies to save water compared to conventional clock timer controllers. The NWS-O model forecasts the amount of water that will be consumed nationally by irrigation systems both with and without the WaterSense program. In developing inputs to the model, LBNL consulted numerous sources, including those described in Dunham et al. 2009, Melody et al. 2014, and Williams et al. 2014. The sources used for the final model values are also described in this report.

This report explains the data LBNL collected and the calculations it used to estimate the water savings associated with WaterSense-labeled WBIC. The calculation of water savings relies on three values: the number of irrigation controllers in use, the market share of irrigation controllers by type (i.e., timers, WBIC, and soil moisture sensors (SMS)), and the water saved annually for WBIC units compared to timers, or unit water savings (UWS). LBNL derives the number of units in use by applying an accounting method to national product shipments and product lifetimes. The market share by type depends on base case and policy case projections of WBIC penetration. The UWS is based on the annual end-use water consumption for homes with automatic irrigation systems, and the percentage of water the WBIC irrigation device saves. To quantify the monetary value of the water savings attributable to the WaterSense-Outdoor program, LBNL also developed prices and price trends for water and wastewater services nationwide.