California State Board proposes new pathogen reduction regulations for water reuse

The State Water Resources Control Board convened on June 6, 2025, for a public hearing regarding the proposed regulations for the onsite treatment and reuse of nonpotable water, designated as SBDDW-22-001. The meeting focused on establishing pathogen log reduction targets and treatment requirements aimed at ensuring public health safety in water reuse practices.

The discussion began with an overview of the pathogen log reduction targets, which are based on risk assessment standards. These targets are designed to minimize pathogen concentrations in source waters to acceptable levels for reuse. The proposed regulations outline specific log reduction targets for various pathogens, including an 8-log reduction for viruses, a 6-log reduction for Giardia, and a 5.5-log reduction for Cryptosporidium in systems intended for indoor use, such as toilet flushing.

The board referenced a 2017 framework developed by the Water Environment and Reuse Foundation, which informed the current recommendations. An expert panel, established by the state board, reviewed this framework and suggested updates based on recent California wastewater pathogen data. The findings of this panel were published in the Journal of Water and Health in October 2022, following an external scientific peer review process.

The proposed regulations also detail two compliance options for treatment trains. The first option involves using preset pathogen control treatment trains that include a combination of membrane bioreactors, membrane filtration, UV disinfection, and chlorination. The second option allows for alternative treatment trains, which must demonstrate equivalent public health protection through a separate approval process.

Additionally, the regulations emphasize the importance of controlling opportunistic pathogens in storage and distribution systems. This includes maintaining temperature control and disinfectant residuals at the farthest end-use fixtures, with ongoing monitoring requirements.

The meeting concluded with a reminder of the public comment period, which is set to end at noon the following day. The state board aims to adopt the regulations by December 31, 2025, with a complete rulemaking package expected by March 20, 2026. Following state board adoption, the Department of Housing and Community Development will develop corresponding building standards within 12 months, aligning with the anticipated 2027 triennial code adoption cycle.

The session transitioned into a public comment period, allowing stakeholders to voice their opinions on the proposed regulations.