New State Water Board Measurement and Reporting Rules: What Water Rights Holders Need to Know by October 2026

California water rights holders should be preparing now for substantial changes to the State Water Resources Control Board’s (State Board) water diversion measurement and reporting framework. Earlier this year, the State Board adopted a rulemaking package that significantly amends prior water diversion measurement and reporting regulations in place since 2016. The revised regulations clarify who must measure water diversions, what must be measured, how data must be submitted, and how the State Board will administer compliance through its new electronic water rights reporting platform, CalWATRS. Persistent drought conditions in California over the past decade underscored the original need to collect accurate data on the volume of surface water diverted by water right holders statewide. The State Board’s revised regulations build on that effort to improve clarity and standardize how measurement data must be submitted.

Although the revised regulations went into effect on February 1, 2026, most of the new water measuring and reporting requirements will take effect at the start of the upcoming 2027 water year on October 1, 2026. That means qualifying water users must update their measurement methodologies and data collection practices by October 1 and maintain compliance thereafter. They will also be required to report measurement data in their annual reports submitted to the State Board beginning with the 2027 water year reports, which will be due January 31, 2028.

The requirements themselves are detailed, and the steps and paperwork necessary will take real lead time to prepare. Below is what to do now, followed by a fuller explanation of the revised rules.

Key Actions and Deadlines for Diverters

If you divert water in California under an appropriative right (pre- or post-1914, permitted, licensed, or subject to a Statement of Diversion and Use) or under a riparian right, here is where to start:

1. Audit and Map Your Portfolio Immediately: Review your complete California water rights holdings to determine which rights meet individual or combined water diversion thresholds (>10 AF/yr) or large diversion thresholds (>10,000 AF/yr or >30 cfs).
2. Review Physical Equipment Accuracy: Coordinate with a qualified professional to test whether your active measurement equipment operates within the prescribed error margins.
3. Draft a Formal Measurement Methodology: Do not wait until the January 31, 2027, deadline to outline your methodology. Begin cataloging quality assurance protocols, conversion calculations, and methodologies used to distinguish measurements between multiple claimed rights, if necessary, for a smooth CalWATRS integration.
4. Establish a Standardized Reporting Workflow: Ensure your diversion and use measurements are tracked and logged in accordance with the applicable frequency standards so that annual data are ready for submission to the State Board by the next reporting deadline of January 31, 2027.
5. Enforce Internal Raw Output Archiving: Update your internal management practices to ensure that raw device output data files are securely archived for the newly mandated 10-year retention window.
6. Calendar the Deadlines: October 1, 2026, and January 31, 2027, are the two dates that matter most; see the table below.
   
   

Approaching Deadlines
October 1, 2026	Install measurement devices compliant with updated requirements. Begin measuring according to updated requirements.
January 31, 2027	Submit annual reports for the 2026 water year (Oct. 1, 2025, through Sept. 30, 2026) to CalWATRS in accordance with previous requirements. Register devices according to updated requirements. Submit measurement methodology.
October 1, 2027	Ensure all required data for the 2027 water year (Oct. 1, 2026, through Sept. 30, 2027) has been collected and is ready to be submitted in the format and frequency required.
January 31, 2028	Submit annual reports for the 2027 water year to CalWATRS in accordance with the updated requirements.

With an immediate to-do list in hand, the rest of this alert works through the details of the State Board’s revised regulations, including who is affected, what must be measured, and how the State Board intends to enforce them.

Who is Affected?

Most of those who must comply with the new regulations have already been measuring their water diversions in accordance with the prior rules. The following groups of surface water rights holders are subject to the new revisions:

1. Anyone authorized to divert greater than 10 acre-feet per year under a State Board-issued permit or a license.
2. Anyone who has previously diverted, or intends to divert, greater than 10 acre-feet of water per year and is required to file a Statement of Water Diversion and Use under Water Code section 5100 et seq.
3. Anyone authorized to divert more than 10 acre-feet of water per year or to maintain a storage facility with a capacity greater than 10 acre-feet.

The regulations apply to pre- and post-1914 appropriative rights to surface water, as well as riparian water rights. Compliance is also triggered if a diverter holds a combination of claimed water rights that either share a point of diversion or divert to the same reservoir, and the sum of those combined maximum allowable diversion amounts exceeds 10 acre-feet per year. The new rules, however, clarify that the 10 acre-foot threshold is based on the greater value of either historical use or the face value of the permit or license. It is not based on the actual amount of water diverted or stored during the current water year. Stockpond certificates, registrations for small domestic use, and cannabis cultivation are entirely exempt from the measurement and reporting requirements.

The revised regulations also created a new set of rules applicable to “large diversions,” which generally refers to actual or authorized diversions of more than 10,000 acre-feet per year or 30 cubic feet per second. Diverters meeting this threshold must comply with all requirements discussed in this alert and are subject to certain additional measurement and reporting obligations.

What Must Be Measured?

The new rules establish a clear set of measurement parameters. Previously, diverters had the option of measuring the total volume of water diverted, flow rate, water velocity, or water elevation. Now, diverters must measure and report both discrete volume and flow rate across direct diversions and diversions to storage. Diverters with a reservoir with a storage capacity greater than 5,000 acre-feet must additionally measure and report the volume and flow rate of water withdrawn from storage and water released, regardless of whether any of that water was stored. The revised rule also authorizes the State Board’s deputy director to require measurement of re-diversions when necessary to understand water supply, demand, or availability.

For many diverters, compliance could require installing new measuring devices and revisiting device configuration, data architecture, and internal accounting practices so that the required parameters are captured in a way that can be translated into compliant data files.

What are the Measurement Frequency and Accuracy Standards?

The State Board has also consolidated and restructured its frequency and accuracy thresholds based on a water right’s maximum allowable diversion or a reservoir’s total storage capacity. For diversion to storage, the frequency depends on storage capacity: when capacity is greater than 1,000 acre-feet, measurements must be collected hourly; when capacity is greater than 200 acre-feet, measurements must be collected daily; when capacity is greater than 50 acre-feet, measurements must be collected weekly; and when capacity is greater than 10 acre-feet, measurements must be collected monthly. No measurement is required for reservoirs with less than 10 acre-feet of storage. For all other water rights, including for direct diversion, diversion to underground storage, or a combination of direct diversion and diversion to surface or underground storage, the frequency of measurements must follow a similar schedule based on the maximum allowable diversion amount under the claimed right using the same 1,000, 200, 50, and 10 acre-foot thresholds to determine hourly, daily, weekly, or monthly measurement intervals. No measurement is required for claims in which the maximum diversion amount allowed is less than 10 acre-feet.

The State Board retained prior measurement accuracy standards but stated them more clearly, generally requiring measurement devices to be between 85 and 90 percent accurate, depending on when the measuring device was installed and how frequently the water diversions must be reported. Diverters must notify the State Board in writing within 30 days after detecting that data do not, or likely will not, satisfy those standards and must promptly repair, replace, or otherwise correct the methodology at the diverter’s expense.

The State Board now ties compliance not just to installation of equipment, but to sustained performance, error detection, notification, and corrective action. Compliance strategies that treat device installation as the end of the process will be inadequate under the new rules.

What Must Be Reported to the State Board?

Another major administrative change is the State Board’s formalization of “measurement methodology” submissions. Section 934 of the State Board’s regulations now requires each diverter to submit detailed information describing its measurement methodology by January 31, 2027, through the State Board’s CalWATRS platform. The measurement methodology description must include the claimed rights covered, points of diversion, measurement locations, measurement devices, conversion formulas used, quality assurance protocols, apportionment methodologies to distinguish diversions attributed to different water rights, and certification by a qualified individual.

The rule also requires diverters to register each measuring device included in the methodology with the State Board and to provide detailed registry information, including make and model, device type, location, measured parameter, units, installation date, and contact information for the qualified individual who installed the device. For active devices used before October 1, 2026, registration must occur by January 31, 2027. Devices first used on or after October 1, 2026, must be registered by the annual report deadline for the first reporting year in which they are used. Those diverters who are already using measuring devices to track their diversions must comply with these registration and measurement methodology requirements by January 31, 2027.

All diverters will be required to follow standardized diversion and use reporting by submitting their hourly, daily, weekly, or monthly diversion and use measurement data, as appropriate, annually to the State Board on a standardized template or by transmitting the data files directly through the CalWATRS platform. Diverters must also retain the raw data from their measurements for at least 10 years. In addition to these annual reporting requirements, large diverters will be required to submit diversion data far more frequently—within 7 days of a qualifying large diversion measurement date.

Enforcement and Severe Daily Penalties

While the State Board has some discretion to adjust thresholds or submission schedules and to allow alternative measurement plans, compliance enforcement has been sharply reinforced under the new text. Any failure to timely implement a measurement methodology, properly maintain physical devices, verify operational accuracy, or update expired Alternative Compliance Plans constitutes an immediate regulatory violation. Violations carry direct civil liability up to the statutory maximum of $10,000 per day that the violation occurs under Water Code section 1846.

The State Board does allow exemptions for unforeseeable disruptions. Diverters whose diversion infrastructure or measuring equipment is destroyed or disabled by a natural disaster, emergency, or other unforeseen event may seek temporary relief from the applicable measurement or reporting obligations. Diverters must act quickly, however, to provide written notice to the State Board within 30 days of the damage and continue measuring everything that remains operational. The exemptions run only as long as the damage persists, generally up to 180 days, and full compliance resumes automatically once that period ends or the equipment is repaired, whichever occurs first.

These changes ensure that the rulemaking is not merely a formatting exercise. The State Board has converted many prior ambiguities into clearer performance and filing obligations, which in turn increases the State Board’s ability to characterize noncompliance as a discrete, enforceable violation.

Concluding Comments

The State Board’s regulatory overhaul marks a clear step toward standardized water tracking and improved statewide water use data. By tying compliance directly to the CalWATRS platform, the state has positioned itself to audit data accuracy with enhanced scrutiny. Diverters must take deliberate, proactive steps during the transition window to safeguard their operations from potential violations.

Please contact the Allen Matkins water law team for more guidance about how the full suite of changes affects your water rights portfolio.