California State Water Board adopts order to protect groundwater from over application of manure at dairies

Advancing the protection of the Central Valley’s drinking water sources while balancing the needs of its agricultural economy, the State Water Resources Control Board adopted new rules to safeguard groundwater quality while providing the dairy industry reasonable timelines to adopt sustainable manure management practices.

California produces more milk than any other state, with most dairy farms located in the Central Valley. The board’s new dairy order will reduce discharges of nitrogen – a natural component of manure that can pose a threat to human health at high concentrations in drinking water. The overapplication of dairy manure to croplands has been shown to harm groundwater supplies in the Central Valley which many communities rely upon for drinking water.

“California’s dairies anchor the Central Valley economy, and many have worked hard on nutrient management over the past decade. This order recognizes that work, and it also recognizes that nitrate is still in household drinking water wells,” said State Water Board Chair E. Joaquin Esquivel. “The order sets legally required outcomes, defines timelines, and obligates dairies to deliver safe drinking water to affected households in the meantime.”

For over a decade the dairy community, drinking water advocates, Central Valley residents have been devoted to the issues that are addressed by this order. Adoption is not the end of the work, but it turns the page to implementation.”

Among other requirements, the order:

• Increasingly limits existing dairies’ application of manure to croplands according to a schedule that is as short as possible, not to exceed 35 years.
• Requires dairies responsible for nitrate impacts to wells to provide alternative drinking water supplies for those households.
• Requires stricter nitrogen monitoring and ensures that dairy manure retention ponds are not leaking at rates that affect groundwater.
• Develops new requirements to prevent unsafe concentrations of nitrate in groundwater.
• Encourages and facilitates the large-scale export of treated manure from dairies to other agricultural lands, where it can be applied at rates that both fertilize crops and protect groundwater.
• Defines timelines for the Central Valley Regional Water Quality Control Board to revise its dairy waste discharge requirements and take other actions to implement the order.

To ensure progress and transparency, the order requires the Central Valley Water Board and the State Water Board’s Division of Water Quality to generate reports every six months that identify upcoming implementation milestones. The reports will provide continuous, rolling tracking of progress made toward the order’s milestones and tasks.

The final order incorporates some of the public comments that were received on previous draft versions that the State Water Board released in October 2024, June 2026 and September 2026, in addition to input accepted during a public workshop held earlier this year and at yesterday’s board meeting.

More information on the dairy order is available on the board’s website.