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2. Water Use Drivers <br />Data drivers for each water use sector are definod in Exbibit 3. <br />tlrhfbit 3. Water Use Drivers by Sector <br />I Water Use Sector , Water Use Driver Source 1 <br />Single Family Numuber of single family RWC Housing Element, <br />dweq= units 1999 -20W <br />Multiple Family I Number of multiple family RWC Housing Element, <br />dwelling units 1 1999.2006; RWC Planning <br />I Commercial I Number of empioyeas ABAG <br />Commercial Irrigation I Number ofemployees , ABAG I <br />Government I Population I ABAG <br />Other I Population I ABAG <br />Residential irrigation I Number of multiple family RWC Housing Element, <br />dwelling units 1 1999-2006; RWC Planning <br />The values of time data drivers are shown in Appendix A in 5-year increments 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 future <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 linking 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 multiplo-farnify 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 />3. Water Use Coefficients <br />The water use coefficients we 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 bow the coefficients are adjusted for each. <br />Page 4 <br />