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Santa Ana 2020 Urban Water Management Plan <br />arcadis.com <br />4-4 <br />For existing residential homes, the current average indoor and outdoor water use for each agency were <br />used for the year 2020. It was assumed that indoor water uses would reach the high efficiency level by <br />2040. Based on current age of homes, replacement/remodeling rates, and water utility rebate programs it <br />is believed this assumption is very achievable. It was also assumed that current outdoor water use would <br />be reduced by 5% by 2050. <br />For new homes, the indoor high efficiency level was assumed for the years 2025 through 2050. Outdoor <br />uses for new homes were assumed to be 25% and 30% lower than current household water use for <br />single-family and multifamily homes, respectively. This methodology is illustrated in Figure 4-1 below. <br />Figure 4-1: Water Use Projection Methodology Diagram <br />Existing and projected population, single-family and multifamily households for each retail water agency <br />were provided by CDR under contract by MWDOC and OCWD. CDR provides historical and future <br />demographics by census tracts for all of Orange County (Section 3.4). Census tract data is then clipped <br />to retail water agency service boundaries in order to produce historical and projected demographic data <br />by agency. <br />For the CII water demands, which have been fairly stable from a unit use perspective <br />(gallons/account/day), it was assumed that the unit demand in FY 2019-20 would remain the same from <br />2020-2025 to represent COVID-19 impacts. Reviewing agency water use data from FY 2017-18 through <br />FY2019-20 revealed that residential water use increased slightly in FY 2019-20 while CII demands <br />decreased slightly as a result of COVID-19. From 2030 to 2050, the average CII unit use from <br />FY 2017-18 and 2018-19 was used. These unit use factors were then multiplied by an assumed growth <br />of CII accounts under three broad scenarios: <br /> Low Scenario – assuming no growth in CII accounts <br /> Mid Scenario – assuming 0.5% annual growth in CII accounts <br /> High Scenario – assuming 1.5% annual growth in CII accounts