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HomeWater CodeDiv. 6Pt. 2.6Ch. 3Art. 2.5§ 10635 Water Supply Reliability Assessment

§ 10635 Water Supply Reliability Assessment

Water Code·California
AI Summary·Official Text·Key Terms·Related Statutes·References
AI SummaryVerified

§ 10635 Water Supply Reliability Assessment

This law makes water companies plan ahead to ensure they have enough water for their customers, even during dry years or long droughts. They must check their water sources and compare them to how much water people will likely use over the next 20 years.

Key Takeaways

  • •Water companies must plan for normal years, dry years, and long droughts.
  • •They have to compare their water sources to how much water people will use over the next 20 years.
  • •If they don’t have enough water, they must make plans to save water or find more.
  • •They also have to share their plans with the cities and counties they serve.

Example

A city's water company looks at how much water they have from rivers, wells, and saved water. They then guess how much water people will use in 5, 10, 15, and 20 years, even if there’s a 5-year drought.

The water company must make sure they won’t run out of water, even if it doesn’t rain for a long time. If they think they might not have enough, they have to plan ways to save water or find more.

How to Calculate

Total Water Supply ≥ Total Projected Water Use (for normal, dry, and 5-year drought periods)

  1. Add up all the water the company gets from rivers, wells, saved water, and other sources.
  2. Guess how much water people will use in 5, 10, 15, and 20 years for normal years, dry years, and a 5-year drought.
  3. Compare the total water supply to the total water people will use. If the supply is less than what people need, the company must plan ways to fix it.

A water company checks if they have enough water for a 5-year drought.

Result: The water company has enough water (100 million ≥ 95 million), so they don’t need to worry. But if the use was 105 million, they’d need to find more water or tell people to use less.

AI-generated — May contain errors. Not legal advice. Always verify source.

Official Source
View on CA.gov

§ 10635 Water Supply Reliability Assessment

(a) Every urban water supplier shall include, as part of its urban water management plan, an assessment of the reliability of its water service to its customers during normal, dry, and multiple dry water years. This water supply and demand assessment shall compare the total water supply sources available to the water supplier with the long-term total projected water use over the next 20 years, in five-year increments, for a normal water year, a single dry water year, and a drought lasting five consecutive water years. The water service reliability assessment shall be based upon the information compiled pursuant to Section 10631, including available data from state, regional, or local agency population projections within the service area of the urban water supplier. (b) Every urban water supplier shall include, as part of its urban water management plan, a drought risk assessment for its water service to its customers as part of information considered in developing the demand management measures and water supply projects and programs to be included in the urban water management plan. The urban water supplier may conduct an interim update or updates to this drought risk assessment within the five-year cycle of its urban water management plan update. The drought risk assessment shall include each of the following: (1) A description of the data, methodology, and basis for one or more supply shortage conditions that are necessary to conduct a drought risk assessment for a drought period that lasts five consecutive water years, starting from the year following when the assessment is conducted. (2) A determination of the reliability of each source of supply under a variety of water shortage conditions. This may include a determination that a particular source of water supply is fully reliable under most, if not all, conditions. (3) A comparison of the total water supply sources available to the water supplier with the total projected water use for the drought period. (4) Considerations of the historical drought hydrology, plausible changes on projected supplies and demands under climate change conditions, anticipated regulatory changes, and other locally applicable criteria. (c) The urban water supplier shall provide that portion of its urban water management plan prepared pursuant to this article to any city or county within which it provides water supplies no later than 60 days after the submission of its urban water management plan. (d) Nothing in this article is intended to create a right or entitlement to water service or any specific level of water service. (e) Nothing in this article is intended to change existing law concerning an urban water supplier’s obligation to provide water service to its existing customers or to any potential future customers. (Amended by Stats. 2018, Ch. 14, Sec. 36. (SB 606) Effective January 1, 2019.)

Last verified: January 11, 2026

Key Terms

urban water supplierwater supply and demand assessmentdrought risk assessmentwater management plan

Related Statutes

  • § 10654 Water Conservation Cost Recovery
  • § 10620 Urban Water Management Plans
  • § 10621 Urban Water Supplier Plan Updates
  • § 10631 Urban Water Management Plans
  • § 10632.1 Urban Water Shortage Reporting

References

  • Official text at leginfo.legislature.ca.gov
  • California Legislature. Water Code. Section 10635.
View Official Source