Greg Wetterau
Susan Brownstein
California’s direct potable reuse (DPR) regulations were adopted by the State Water Resources Control Board on December 19, 2023, and are expected to be effective in 2024 when they are officially incorporated into Title 22 of the California Code of Regulation (CCR).
With more than 1.3 billion gallons per day of wastewater effluent being discharged into the Pacific Ocean by California wastewater utilities, the DPR regulations provide an opportunity for increased beneficial use of our wastewater flows and a pathway to developing new drought-proof water supplies and diversified water supply portfolios throughout the state.
The DPR regulations represent the culmination of years of research, stakeholder engagement, and expert review panels that began with Senate Bill 918 in 2010 and the State Water Board’s preliminary report on the feasibility of developing uniform water recycling criteria for DPR in 2016.
Unlike groundwater recharge and surface water augmentation within the state’s indirect potable reuse (IPR) regulations, DPR has little or no environmental barrier between the advanced treatment process and drinking water customers. Instead, DPR regulations require a higher level of treatment, operator certification, and monitoring and reporting to ensure protection of public health.
Because the primary endpoint is drinking water customers and not discharged into the environment, the Division of Drinking Water (DDW) oversees DPR permitting and oversight, not the State’s Regional Water Quality Control Boards (RWQCB).
In addition to these technical requirements, the DPR regulation requires the formation of a “direct potable reuse responsible agency,” or DiPRRA, which is defined as the public water system responsible for compliance for a DPR project.
Utilities and agencies responsible for wastewater collection and treatment are considered partner agencies to the DiPRRA, and only a DiPRRA can receive a DPR permit because DDW can only issue enforcement actions to public water systems.
Without an environmental barrier, the DPR regulations place requirements on the DiPRRA to ensure timely and clear communication and accountability between all agencies that signed on for the DPR project.
The DiPRRA is expected to “enable and facilitate the inspection by the State Board at any time of all facilities, operations, and records” used in the DPR project (CCR Section 64669.10) and develop a detailed “Joint Plan” that is signed by each partner agency (CCR Section 64669.20).
Similar to requirements in the IPR regulations, DPR requires full advanced treatment with reverse osmosis (RO) and advanced oxidation (AOx), with additional requirements for both chemical reduction and pathogen removal.
Chemical reduction must be done with a minimum of three processes using three distinct removal mechanisms and must include ozone and biologically active carbon (BAC) upstream of RO and AOx.
Pathogen reduction must be done with a minimum of four processes using three distinct mechanisms, including membrane separation, ultraviolet (UV) disinfection, and chemical inactivation.
Pathogen removal must also achieve a minimum reduction of 20-log virus, 14-log giardia, and 15-log cryptosporidium at least 90% of the time.
Alternative treatment approaches can be proposed and blending with other water sources can be used for chemical reduction and pathogen reduction credits. Because of the RO treatment requirement, DPR may be challenging for inland utilities without affordable brine disposal options.
While the alternatives clauses could open the door for non-RO options, stringent requirements for TOC removal, pathogen reduction, and chemical reduction would make DPR without RO difficult to permit.
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