June 4, 2026
To: WaterSupplyPlanning@valleywater.org
CC: Valley Water Board of Directors and Clerk of the Board
Re: Sierra Club Comments on Valley Water’s Draft 2025 Urban Water Management Plan (June 9, 2026, Agenda Item 3.5. Public Hearing on the 2025 Urban Water Management Plan and Water Shortage Contingency Plan)
The Sierra Club Loma Prieta Chapter has reviewed Valley Water’s Draft 2025 Urban Water Management Plan (UWMP). Please consider the following comments regarding the Draft UWMP which focus on water demand projections, and specifically the evidence that water use will continue the current downward trend and how that could impact water supply planning.
Demand Projections
On February 23, 2026 the Water Supply and Demand Management Committee (WSDMC) meeting included an item to receive Information on 2025 UWMP update and provide feedback. The Sierra Club submitted the attached comment letter to the Committee regarding the Water Supply Master Plan 2050 demand projections to be used in the UWMP.
Our comment letter discusses the historic inaccuracy of demand projections in Valley Water’s UWMPs since 2000, and introduces a model we created that fits more closely to historic demands, and projects demand continuing to decrease in the future. Looking back, we found that UWMP forecasts have over-projected future demand by about 50% on average since 2000.
This trend of declining demand is supported by UWMP Figure 4-5, which shows reduced water usage in 2025 compared to 2024. However, the UWMP still projects a steep increase in demand between 2026 and 2030 from about 280,000 acre-feet/year (AFY) to 330,000 AFY. This is about an 18% increase in water demand over four years. Considering Valley Water’s conservation goal to reduce demand by 12,000 AFY during the same period, this would actually be a 23% increase in demand, which does not seem realistic.
The forecasted sharp increase in demand to 330,000 AFY by 2030, and then stable demand through 2050 was described in a September 2023 memo titled “Water Supply Master Plan Demands.” At a minimum, baseline data (such as actual population growth and actual water demand) have changed in the past two and a half years. The Draft 2025 UWMP uses this same demand forecast, which is now out-of-date and needs to be recalculated as soon as possible.
Following submission of the attached comments, the Sierra Club met with Valley Water staff from the water supply planning team to discuss water demand projections and Valley Water’s demand forecasting model. We learned more about the data and assumptions used to run the model, and we were impressed by the comprehensiveness of the model. However, we still don’t understand how the model shows a steep increase in water demand from 2025 to 2030.
Therefore, we made a public record request for the demand modeling files, but thus far the records have not been provided due to their location offsite and the need for legal review. These delays hamper our ability to fully analyze the demand modeling for the 2025 UWMP.
Consultant Studies on Water Use Projections and Demand Elasticity
On March 23, 2026 the WSDMC received the results of a consultant study regarding Valley Water’s water use projections. The consultant’s technical memorandum says the result of their analysis “indicates a clear downward trend in water usage, likely influenced by conservation efforts and behavioral shifts.”
The consultant also completed a water demand elasticity analysis. Their memorandum on elasticity concludes that price increases will result in downward pressure on demand, predicting that “a 10% increase in price would be expected to reduce retail demand by about 2%.”
The Protection and Augmentation of Water Supplies report for 2026-27 projects Valley Water’s wholesale water rates will increase 81% for the North County W-2 zone over the next 10 years. Using the information about elasticity, this would result in at least a 13% decrease in demand over the next 10 years. This accounts for the finding that 83% of wholesale prices pass through to volumetric retail rates, but does not account for the fact that rate increases are cumulative. This impact on demand has yet to be added to Valley Water's models along with drought and conservation, as recommended in the elasticity study.
2026 Demand Trend
In May 2026, the Valley Water Audit Committee received the Fiscal Year 2025-2026 Third Quarter Financial Status Update. During this update, staff reported that groundwater production charges and treated water revenue are estimated to be about $10M below budget due to lower-than-anticipated demand. Although this does not include water delivered by the San Francisco Public Utilities Commission, this shows that water demand is certainly not increasing at the rate projected in the Draft 2025 UWMP.
Appendix H. Reduced Reliance on the Delta
Section H.2, Regional Self Reliance, says “Water supplies that contribute to regional self-reliance are shown in Table C-3. Consistent development and funding of these supplies have resulted in reduced reliance on the percentage of water supplies imported from the Delta watershed as compared to overall water use in the County.”
Please note:
The Draft 2025 UWMP provided for review did not include Tables C-2, C-3 and C-4 which are referenced in the UWMP text, so we cannot comment on the content of those tables.
Since water demand has decreased overall since 2010, the reduced reliance on the Delta as a percentage of water supplies should also result in a volumetric reduction in water supplies imported from the Delta. This should be stated in section H.2, or the lack of a volumetric reduction of imported water (despite decreasing water use) should be explained. Also see section H.3.3, Water Supplies Contributing to Regional Self Reliance which quantifies expected local supplies to be generated from programs to increase water use efficiency, water recycling, potable reuse, etc.
Conclusion
Recent studies and water use data supports the results of Sierra Club’s modeling, which shows water demand will continue to decrease in Santa Clara County. Contrary to demand increases projected in the UWMP, it appears that water use in the County is no longer rebounding from the 2020-2022 drought. However, this information is not reflected in the UWMP water demand forecasts.
By discounting the scenario which continues the downward trend in water usage, Valley Water is not planning for that possible future scenario. Decreasing demand would require larger rate increases, and these rate increases would likely encourage further demand reduction and further unplanned rate increases, etc. This would also impact water affordability for lower-income residents. These possible impacts should be analyzed and quantified.
Therefore, the Sierra Club recommends using a broader range of scenarios for long-term supply/demand planning, including scenarios that use reasonable alternative assumptions related to growth and climate impacts.
Sincerely,
Sue Chow, Chapter Chair
Sierra Club Loma Prieta Chapter
February 20, 2025 comment letter: Demand Scenarios for 2025 Urban Water Management Plan