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Santa Ana 2020 Urban Water Management Plan <br />arcadis.com <br />4-3 <br />Water Use Projections <br />A key component of this 2020 UWMP is to provide an insight into the City’s future water demand outlook. <br />This section discusses the considerations and methodology used to estimate the 25-year water use <br />projection. Overall, total water demand is projected to increase 1.0% between 2020 and 2045. While <br />both single residential use is projected to decrease, multifamily residential use and usage by CII are <br />projected to increase. Demands for large landscape applications are projected to increase. Non-revenue <br />water is projected to decrease in the same period. <br />4.3.1 Water Use Projection Methodology <br />In 2021, MWDOC and OCWD, in collaboration with member agencies and MET member agencies, led <br />the effort to update water demand projections originally done as part of the 2021 OC Water Demand <br />Forecast for MWDOC and OCWD. The updated demand projections, prepared by CDM Smith, were for <br />the Orange County region as a whole, and provided retail agency specific demands. The projections span <br />the years of 2025-2050 and are based upon information surveyed from each Orange County water <br />agency. <br />The forecast methodology began with a retail water agency survey that asked for FY 2017-18, <br />FY 2018-19 and FY 2019-20 water use by major sector, including number of accounts. If an agency <br />provided recycled water to customers that information was also requested. Given that FY 2017-18 was a <br />slightly above-normal demand year (warmer/drier than average) and FY 2018-19 was a slightly <br />below-normal demand year (cooler/wetter than average), water use from these two years were averaged <br />to represent an average-year base water demand. <br />For the residential sectors (single-family and multifamily) the base year water demand was divided by <br />households in order to get a total per unit water use (gallons per home per day). In order to split <br />household water use into indoor and outdoor uses, three sources of information were used, along with <br />CDM Smith’s expertise. The sources of information included: (1) the Residential End Uses of Water <br />(Water Research Foundation, 2016); (2) California’s plumbing codes and landscape ordinances; and <br />(3) CA DWR’s Model Water Efficient Landscape Ordinance (MWELO) calculator. <br />Three different periods of residential end uses of water were analyzed as follows: <br />Pre-2010 efficiency levels – Has an average indoor water use that is considered to be <br />moderately efficient, also does not include the most recent requirements for MWELO. <br />High-efficiency levels – Includes the most recent plumbing codes that are considered to be <br />highly efficient, and also includes the most recent requirements for MWELO. <br />Current average efficiency levels – Represents the weighted average between pre-2010 <br />efficiency and high efficiency levels, based on average age of homes for each retail water <br />agency. <br />For outdoor residential water use, the indoor per capita total was multiplied by each agency-specific <br />persons per household in order to get an indoor residential household water use (gallons per day per <br />home), and then was subtracted from the base year total household water use for single-family and <br />multifamily for each agency based on actual water use as reported by the agency surveys.