Water Measurement Regulation

California's recent droughts have highlighted the need for more current and accurate water diversion data on a statewide scale. Previous standards required monthly diversion amounts be reported annually, but the 2012-2016 drought highlighted the limitations of such standards and their application to drought management. Even in non-drought years, rainfall and snow patterns vary widely. Adequate supply in some regions may occur at the same time as critical water shortages elsewhere, and these patterns can change throughout the year. High quality, accurate data that is collected and reported at a finer resolution is therefore essential for managing water resources throughout the state. Accurate reporting protects your water rights, helps inform both statewide and local water availability and future planning decisions, and assists in processing water right applications.

Measurement data helps improve the way California manages and allocates water rights by helping to

• Forecast and plan for limited water supplies
• Ensure compliance with permit and license terms of existing water rights
• Protect water rights based on priority year
• Provide for efficient management and use of water during times of shortage
• Improve water planning and near-term forecasting of water demand
• Facilitate collaborative solutions between the State Water Board and local water managers

In general, those who divert more than 10 acre-feet per year are required to measure and report their diversions. This includes diverters who have

• A single water right with a face value or historical use (whichever is greater) of more than 10 acre-feet per year
• Multiple water rights that share either a point of diversion, place of use, or divert to the same reservoir and have a combined face value or historical use of more than 10 acre-feet per year
• A storage facility with a capacity of more than 10 acre-feet

Note: The 10-acre-foot threshold is based on the greater value of historical use or face value. It is not based on the amount of water diverted or stored during the current reporting year. If you are unsure of the details of your water right or claim of right, please refer to the following guide: Know Your Water Right.

Refer to the Water Year 2026 Measurement and Data Submission Manual for more information on who needs to measure their diversions.

Diverters must measure and report their diversion volumes by water right. In general, measurements must be accurate to within ±10 to 15 percent, depending on the size of the water right. Refer to the Water Year 2026 Measurement and Data Submission Manual for more information on measurement and accuracy requirements.

Diverters must measure each of the following, as applicable:

• Volume of water directly diverted under each water right
• Volume of water diverted to storage under each water right
• Volume of water withdrawn and/or released from storage under each water right

For reservoirs that operate in a pattern of drawdown and refill, diverters must also record each of the following:

• Maximum and minimum water surface elevation during each drawdown-refill cycle
• Reservoir volumes corresponding to these elevations
• Dates of these measurements

Diverters must measure their diversions using a measuring device, measurement method, or combination of devices and/or methods. The terms “measuring device” and “measurement method” have specific definitions in the context of this regulation that are described below. Refer to the Water Year 2026 Measurement and Data Submission Manual for more information about measuring devices and measurement methods.

Measuring devices can be any devices, including custom or in-house built devices, that directly measure either volume, flow rate, water velocity, or water elevation. Diverters must then use the measured value to calculate the volume of water diverted. On or before January 31, 2027, diverters must register each of their measuring devices in CalWATRS. Examples of measuring devices are shown in the table below. For your convenience, the State Water Board has a list of measuring device vendors.

Measurement methods are any other way of measuring diversions that do not use a “measuring device” (as defined above) to measure the volume of water diverted under a single water right. Usually, a measurement method will require some math to calculate the volume of water diverted for each water right. Here are some examples of measurement methods:

• A group of diverters each divert water from the same location, but they share a flow meter. Even though a flow meter meets the definition of a measuring device, a measurement method is needed to determine the volume diverted under each water right. The meter measures the total amount of water they all divert, so they use a measurement method to calculate the amount of water that is diverted under each of their water rights.
• A diverter uses a pump to divert water from a stream. The pump has its own dedicated electricity meter and operates at a constant rate. The diverter uses the electricity records combined with the pump specifications and pump curve to calculate the volume of water diverted.
• A diverter pumps water into a storage tank and only refills the tank when it empties. The diverter counts the number of times the tank is filled and multiplies that by the volume of the tank to calculate the volume of water diverted.

Diverters must have previously submitted a measurement method to the Board before February 1, 2026. Any measurement method on file with the Board may remain valid through September 30, 2026.

Below are some additional resources for measuring diversions:

• U.S. Bureau of Reclamation Water Measurement Manual
• Fact Sheet: Pipes and Closed Conduits
• Fact Sheet: Open Channels (including weirs, flumes, canal meter gates, non-standard structures)
• Fact Sheet: Wells
• Fact Sheet: Low Flow Rates (including battery-operated flow meters, volumetric calculations by stopwatch, pump electricity kW-h meters)
• Fact Sheet: Reservoir Diversions to Storage (including water balance calculations, measuring reservoir storage, depth-capacity curve, small reservoirs on ephemeral streams, monthly or manual water level measurement)
• Reservoir Storage Measurement and Recordkeeping Guide for Above-Ground Reservoirs (including installing a measuring device, creating a reservoir capacity curve)
• Average Cost of Measurement (last updated February 2016)
• Financial Assistance Programs (last updated November 2015)

There may be certain situations where a diverter is unable to measure their diversion as frequently or accurately as they are required, including if doing so would be unreasonably expensive, unreasonably affect public trust resources, result in wasted water, or otherwise be infeasible. In such cases, diverters may submit and implement an Alternative Compliance Plan (ACP). Diverters who measure and report under an ACP must meet their specified measurement requirements as much as possible and explain why they are unable to fully meet all requirements. Diverters who previously submitted an ACP before February 1, 2026 may continue using their existing ACP through September 30, 2026. All diverters pursuing alternative compliance must submit an ACP through CalWATRS on or before January 31, 2027 (regardless of whether they submitted a prior ACP before February 2026).

Diverters must measure their diversions monthly, weekly, daily, or hourly, depending on the type and size of diversion. Refer to the table below for more information regarding how frequently to measure diversions. In general, diverters only need to submit their measurement data to the State Water Board once per year. Data is submitted as an attachment to Annual Water Diversion and Use Reports. Optional data file templates are available. Refer to the Water Year 2026 Measurement and Data Submission Manual for more information on measurement frequency requirements.

Diverters should compile measurement data in a data file and submit it as an attachment to their Annual Water Diversion and Use Reports. For detailed information on how to submit data, please refer to the Water Year 2026 Measurement and Data Submission Manual.

Optional data file templates are available below. The State Water Board highly recommends using the provided templates to reduce unintentional reporting errors, ensure that submitted data files include all required components, and ensure that data files are in an appropriate and readable format. For diverters who opt to use a data file format other than what is presented in the provided templates, please refer to the Data File Best Practices and Data File Practices to Avoid sections below for general guidelines on how data files should be structured.

Data File Templates for Measurement Reporting

• Diversion to Direct Use
• Diversion to Storage
• Withdrawals from Storage Use
• Releases from Storage Facility (Outflow)
• Volume in Storage

Data File Best Practices

In general, data files should contain the following information:

1. File type that can be opened using either Microsoft Excel or Microsoft Access (common file types include.xls, .xlsx, .csv, .txt, .dat)
2. Descriptive column headings in the first row of the data file
3. Use only one spreadsheet “tab” with only one data table per data file (you may submit multiple data files with your Annual Water Diversion and Use Report)
4. Date and time of measurement
5. Measured value (the raw/unaltered data output from your measuring device or measurement method)
6. At a minimum, include the volume of water diverted under the water right at each time stamp (any calculation or conversion protocols should be attached separately to your Annual Report and not included within your data file). Best data practice is to also include flow rate of diversion. If the measured value has known or suspected errors, the values in the Volume and Flow Rate columns may be based on quality assured data.
7. Units written out in their entirety (i.e., not abbreviated)
   • Any standard units are acceptable. Common examples include acre-feet or gallons (for volume), cubic feet per second or gallons per day (for flow rate), feet per second (for water velocity), and feet or meters (for water elevation).

Data File Practices to Avoid

In general, data files should not contain the following:

1. Images or graphs, or file types that are not machine readable, such as .pdf, .jpg, .png, .bmp, etc.
2. Unclear or missing column headings
3. Multiple data tables in a single data file
4. Multiple spreadsheet “tabs”
5. Merged cells or multiple values within the same cell
6. Irrelevant data that does not relate to diversion measurements
7. Excessive narrative text
8. Hyperlinks to external databases

Each diverter must register their measuring devices in CalWATRS and submit a measurement methodology that describes how they collect, interpret, and process the raw data from their measuring devices to meet the measurement requirements. This may include descriptions of:

• How to calculate the volume and flow rate of water directly diverted, diverted to storage, withdrawn from storage, and released from a reservoir, as applicable
• How to quality control the measurement data to meet the accuracy requirements,
• How to apportion measurements to each claimed water right, and
• Any other procedure used to convert the raw device output into a general measurement data file or large diversion submission.

Diverters must register measuring devices and submit a measurement methodology through CalWATRS by January 31, 2027. Measurement methodologies are subject to review, but are presumed to be approved upon submission, unless a written rejection has been issued.

Measuring diversions can be complex, therefore a qualified individual must ensure that your diversions are measured accurately. A qualified individual is always required, regardless of whether the diversion is measured using a measuring device, measurement method, or Alternative Compliance Plan. However, the exact role the qualified individual performs varies depending on how the diversion is measured. Refer to the Water Year 2026 Measurement and Data Submission Manual for information on qualified individuals and when they are needed.

The following table summarizes who is eligible to become a qualified individual based on diversion size:

Most diverters may find it easiest to hire a qualified individual to help measure their diversions. For your convenience, the State Water Board maintains a list of consultants that practice in water rights. Note: The State Water Board does not endorse any of the professionals on these lists and you may find other professionals that suit your needs.

The following instructional courses are approved for becoming a qualified individual:

• Assembly Bill 589 Training Classes offered through the University of California, Agriculture and Natural Resources

For future annual reports, starting with water year 2027 reports (due by January 31, 2028), requirements are based on the updated version of the regulation. Below is information on the updated regulation's measuring and data submission requirements.

The State Water Resources Control Board's primary water rights enforcement goal is to encourage compliance with the water rights priority system. This includes taking actions against unauthorized diversions, diversions that adversely impact fish and wildlife, violations of curtailment orders, and more.

The progressive enforcement flowchart provides a general visualization of the Division of Water Right's enforcement process. The State Water Board understands that it may take time for diverters to come into compliance with the revised regulation. The Board will work with diverters who have difficulty coming into compliance with the regulation.

You can find more information about the Board's enforcement procedures here.

The Water Measurement Regulation (previously known as the Measuring and Monitoring Regulation) was adopted in 2016, and most requirements have been in effect since 2018 or earlier. Prior to being updated in 2026, the regulation lacked clear requirements regarding what diverters needed to measure and how they needed to format their data files. As a result, diverters struggled to comply with the regulation and non-standardized data files meant that the State Water Board was unable to efficiently and systematically analyze diversion data to make data-informed decisions. In 2025, the State Water Board began the rulemaking process to formally revise the regulation to clarify requirements and align the regulation with the California Water Accounting, Tracking, and Reporting System (CalWATRS). After being approved by the Office of Administrative Law, the revised Water Measurement Regulation was added to the California Code of Regulations on February 1, 2026. For more information about the rulemaking process to revise the regulation, please visit the Water Measurement and Reporting Rulemaking webpage.