2025 Orange County Water Demand Projection Model
Executive Summary The Municipal Water District of Orange County (MWDOC) supplies water to 26 retail agencies, and the Orange County Water District (OCWD). The Orange County demand forecasts include the MWDOC service area as well as 3 cities who are direct customers of the Metropolitan Water District of Southern California (MWD): Anaheim, Fullerton, and Santa Ana. Water demand forecasts are a foundational element of water supply and infrastructure planning, and MWDOC and OCWD selected Hazen and Sawyer (Hazen) to update the demand forecasts for Orange County's retail agencies for the 2025 Urban Water Management Plan. The update is necessary both because current demands are lower than previously projected, and new demographic and climate projections were made available in 2025. Hazen created four demand models for each Orange County retail agency. The four models represent demand sectors in which agency billing sector uses are similar in magnitude, and in which changes in billing sector water use can be attributed to the same variables. The four sectors are:
1) Single-family Residential
2) Multifamily Residential
3) Commercial, Industrial, and Institutional (CII)
4) Dedicated Irrigation (potable, recycled & raw water)
The demand across all four models, plus other uses for each agency, is summed to a total forecast for each agency, the MWDOC service area, the OCWD service area, and total Orange County.
Econometric Approach and Data Acquisition
A regression, or econometric, approach to demand forecasting statistically links retail level water use to weather, economic, and socioeconomic factors (explanatory variables). Orange County agencies provided comprehensive datasets of historical water use, and Hazen worked with MWDOC to obtain explanatory variables from reputable sources, including weather databases and Census-based reports. The explanatory variables used in the regression are based on Hazen’s experience regarding what factors affect water use nationwide and in Southern California. By statistically linking water use to explanatory variables, econometric models provide a robust foundation for understanding variability and projecting future consumption patterns. Modeled water use is the product of the driver count, and the rate of water use per driver ( Equation ES-1 ).
Equation ES-1
𝑊𝑎𝑡𝑒𝑟 𝑢𝑠𝑒 = 𝐷𝑟𝑖𝑣𝑒𝑟 𝐶𝑜𝑢𝑛𝑡 ∗ 𝑅𝑎𝑡𝑒 𝑜𝑓 𝑈𝑠𝑒 𝑝𝑒𝑟 𝐷𝑟𝑖𝑣𝑒𝑟
Driver units change into the future based on housing, employment, and population projections. The rate of water use per driver is based on the historical response of the use rate to explanatory variables (measured by coefficients) and the future values of those same explanatory variables. Equation ES-2 shows an example use per account, where water price and temperature are examples of explanatory variables, and C Intercept , C R , and C T are example coefficients.
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Appendix G - 10
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