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Section 4 | Water Use Characterization
Law
10631. A plan shall be adopted in accordance with this chapter and shall do all of the following:
10631(d)(1) Quantify, to the extent records are available, past and current water use, over the same five-year increments described in subdivision (a), and projected water use, based upon information developed pursuant to subdivision (a), identifying the uses among water use sectors including, but not necessarily limited to, all of the following: (A) Single-family residential. (B) Multifamily. (C) Commercial. (D) Industrial. (E) Institutional and governmental. (F) Landscape. (G) Sales to other agencies. (H) Saline water intrusion barriers, groundwater recharge, or conjunctive use, or any combination thereof. (I) Agricultural. (J) Distribution system water loss.
(2) The water use projections shall be in the same five-year increments described in subdivision (a).
(3) (A) The distribution system water loss shall be quantified for each of the five years preceding the plan update, in accordance with rules adopted pursuant to Section 10608.34. (B) The distribution system water loss quantification shall be reported in accordance with a worksheet approved or developed by the department through a public process. The water loss quantification worksheet shall be based on the water system balance methodology developed by the American Water Works Association. (C) In the plan due July 1, 2021, and in each update thereafter, data shall be included to show whether the urban retail water supplier met the distribution loss standards enacted by the board pursuant to Section 10608.34. 10631.1(a) The water use projections required by Section 10631 shall include projected water use for single-family and multifamily residential housing needed for lower income households, as defined in Section 50079.5 of the health and Safety Code, as identified in the housing element of any city, county or city and county in the service area of the supplier. As previously described in Section 3, the foundation for IRWD’s customer water use, water demand forecasting, and planning is the compilation of land use data in the Water Resources Master Plan (WRMP). Solely for the purpose of IRWD’s 2025 UWMP, IRWD utilized demand forecast data aligned with regional data developed by MWDOC. In 2025, MWDOC developed a water demand forecast model for its service area that estimates water demand at the individual retail water agency level, which statistically correlates municipal and industrial (M&I) water use with demographic, socioeconomic, conservation, and weather variables. The methodology links water use to a set of explanatory variables through a regression, or econometric, model. IRWD’s normal or average year water use projections are based on the 2025 Orange County Water Demand Projection Model Technical Memorandum
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IRWD – 2025 Urban Water Management Plan
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