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2. Water Use Drivers <br /> <br />Data drivers for each water use sector are defined in Exhibit <br /> <br /> Exhibit 3. Water Use Drivers by Sector <br /> <br />Water Use Sector Water Use Driver Source <br />Single Family Number of single family RWC Housing Element, <br /> dwelling units 1999-2006 <br />Multiple Family Number of multiple family RWC Housing Element, <br /> dwelling units 1999-2006; RWC Planning <br />Commercial Number of employees ABAG <br />Commercial Irrigation Number of employees ABAG <br />Government Population ABAG <br />Other Population ABAG <br />Residential Irrigation Number of multiple family RWC Housing Element, <br /> dwelling units 1999-2006; RWC Planning <br /> <br />The values of these data drivers are shown in Appendix A in 5-year incremems over the <br />forecast period. These dwelling unit, employee, and population estimates are the best <br />current information available. They can and should be updated as expectations of furore <br />circumstances change. <br />For the single-family residential class, dwelling units are segmented into six categories <br />based on the year the dwelling unit was constructed. Water use patterns are known to <br />vary with vintage based on factors such as water fixture efficiency and size of landscape. <br />We obtained year built by obtaining tax assessor information from San Mateo County <br />and link~ng this information with the water use billing data via parcel number. We <br />defined the categories, partly, to match the years associated with key plumbing code <br />changes. <br />For the multiple-family residential class, dwelling units are segmented into three <br />categories based on the number of dwelling units at a site. The categories include homes <br />with 2 to 4, 5 to 25, and over 25 dwelling units. Water use patterns are known to vary <br />with the number of units at a site based on factors relating to demographics and <br />landscaping. We were not able to obtain year built information for each account in this <br />sector. <br /> <br />3; Water Use Coefficients <br /> <br />The water use coefficients are based on analysis of historical water use billing records. <br />The coefficients mirror the water use driver framework. We investigated adjusting the <br />coefficients for weather, water prices, and water conservation technologies. The sections <br />below describe how the coefficients are adjusted for each. <br /> <br /> Page 4 <br /> <br /> <br />