Development of direct potable reuse regulations in California

California is considering direct potable reuse © DutcherAerials /

Given the pressures on water resources that it faces, California has been a leader in water reuse. Jeff Mosher outlines how the state is planning to take this further by developing regulations to cover direct potable reuse.

Communities in California have predominantly relied on groundwater and surface water sources to meet their demands. However, these public water supplies have been augmented for decades by planned potable reuse through groundwater recharge and, more recently, surface water augmentation. For future potable reuse projects to be successful, however, communities are considering direct potable reuse (DPR) – the planned introduction of recycled water directly into a public water system or into a raw water supply immediately upstream of a water treatment plant – to augment their drinking water supplies. To meet future DPR needs of the state, new regulations are currently under development by California’s State Water Resources Control Board (SWB).

Currently, indirect potable reuse of municipal wastewater is being implemented widely across California, including new groundwater recharge and surface water augmentation projects. In addition to traditional factors such as stressed supplies, population growth, and competition for existing water supplies, other factors are driving large increases in water recycling in the state, including more frequent and severe droughts, increasingly stringent wastewater water quality regulations, potential future discharge restrictions, the desire for more sustainable and reliable water supplies consistent with a One Water approach, and the need to address climate resiliency.

DPR has been implemented in Texas and DPR regulations have been approved in Arizona. In addition, other states are in the process of developing DPR regulations, including Colorado and Florida. California began to evaluate DPR as a viable approach in 2010, and has been steadily moving towards formal regulations through a process that includes legislation and support by water utilities. The Water Board is responsible for developing the regulations through evaluating science, technical, and public health issues. The legislation passed to support this requires that DPR regulations be finalised by 2023.

Current California potable reuse regulations

California has potable reuse regulations for both groundwater recharge and surface water augmentation. Those emphasise the use and benefits of environmental buffers for treatment and provision of a response time in case of a process failure.

Groundwater recharge projects in California were first implemented on a case-by-case basis in the late 1960s, to support seawater intrusion barriers along the coastline and to recharge aquifers. Long-running groundwater recharge projects by the Los Angeles County Sanitation Districts and the Orange County Water District provided operational experience that supported the adoption of final regulations for Groundwater Replenishment Recharge Projects (GRRP) in 2014. A number of groundwater recharge projects are currently being implemented by utilities throughout the state.

Surface Water Augmentation (SWA) regulations were finalised in 2018 to allow recycled water for augmenting surface water reservoirs. In a SWA project, pathogen control can be achieved through the reservoir, advanced treatment, and drinking water treatment. Currently, SWA projects in California include Pure Water San Diego, East County Advanced Water Purification, and Las Virgenes-Triunfo Pure Water Project.

The GRRP and SWA regulations include criteria to ensure public health protection of these projects. These criteria include:

  • Enhanced source control beyond standard pretreatment programmes
  • Wastewater treatment
  • Advanced treatment
  • Water quality requirements, including pathogen and chemical control
  • Monitoring requirements

SWA projects and GRRP projects relying on direct injection require full advanced treatment (FAT), which includes reverse osmosis and advanced oxidation treatment processes.

DPR in California

DPR, which involves using wastewater as a source for drinking water in the absence of a significant environmental buffer, such as a groundwater basin or large reservoir, is the planned introduction of recycled water directly into a public water system or into a raw water supply immediately upstream of a water treatment plant. In California, two forms of DPR have been defined: Raw Water Augmentation (RWA) – Fig 1, the planned placement of recycled water into a system of pipelines or aqueducts that deliver raw water to a drinking water treatment plant that provides water to a public water system; and Treated Drinking Water Augmentation (TWA) – Fig 2, the planned placement of recycled water into the water distribution system of a public water system.

Figure 1. Raw Water Augmentation
Figure 2. Treated Drinking Water Augmentation

Proposed DPR Framework

Based on the legislative mandates, SWB is developing criteria including the following efforts:

  • Publish a DPR Framework
  • Develop DPR criteria using information from recommended DPR research.
  • Establish an expert review panel to review the proposed criteria to ensure that the proposed criteria would protect public health.

DPR research

In reviewing the feasibility of DPR criteria, SWB identified areas of additional investigation pertaining to the control of pathogens and chemicals that would address data gaps needed to develop DPR criteria and regulations in California. SWB collaborated with the Water Research Foundation (WRF) in conducting the research, which was used in the development of DPR criteria. The research projects included:

  • Tools to evaluate quantitative microbial risk and plant performance/reliability
  • Measuring pathogens in wastewater
  • Collecting pathogens in wastewater during outbreaks
  • Defining potential chemical peaks and management options
  • Evaluating analytical methods for detecting unknown chemicals in recycled water

The research has been completed, and the final research reports are available on WRF’s website (


SWB, which has the responsibility for developing DPR regulations in California, published, revised, and amended A proposed framework for regulating direct potable reuse in California (SWRCB 2018, SWRCB 2019, SWRCB 2021).

Building on the criteria for GRRP and SWA, the DPR Framework expands on specific elements, but also includes a number of new requirements, including the following:

  • Joint Plan describing roles of all partner agencies
  • Technical, managerial, financial capacity
  • Operator certification
  • Wastewater source control
  • Pathogen and chemical control
  • Water safety plan
  • Additional monitoring and monitoring plan
  • Engineering report and operations plan
  • Pathogen and chemical control point monitoring and response plan
  • Cross-connection control
  • Corrosion control and stabilisation
  • Public health surveillance.

The DPR Framework and the Addendum, as well as other information, is available on SWB’s website at

Proposed DPR criteria highlights

The proposed DPR criteria in the DPR Framework are extensive. However, areas of high interest include pathogen and chemical control, and the wide range of implementation requirements, such as plans and reporting.

“Groundwater recharge projects in California were first implemented on a case-by-case basis in the late 1960s”

The Framework includes a significant increase in treatment and water quality requirements. The advanced treatment must include four unit processes (versus three processes for GRRP and SWA). The unit processes must include three process mechanisms, including UV disinfection, physical separation, and chemical disinfection. In addition to FAT (reverse osmosis and advanced oxidation), which is required for certain GRRP and SWA projects, ozone/biologically activated carbon will be required for DPR before FAT.

As shown in Table 1, the proposed pathogen requirements for DPR are 20-log reduction values (LRVs) for viruses, 14 LRVs for Giardia, and 15 LRVs for Cryptosporidium. These log removals include extra log reductions for DPR to address reliability.

The DPR Framework includes extensive implementation requirements related to project development, start-up, and compliance and reporting. Table 2 provides a list of some of the requirements.

Potential issues for utilities

The DPR Framework and Addendum present proposed criteria and will be finalised by SWB by the end of 2023. The criteria are currently under review by an Expert Panel. During this review, SWB has received comments on the proposed criteria. Some of the areas that have received comments include the following:

Differentiating RWA and TWA. It appears that the proposed criteria impose the same requirements for both RWA and TWA. However, elements in RWA enhance public health protection. Can these differences result in credit for RWA for the additional public health protection?

Pathogen LRV requirements. The LRVs are higher than GRRP and SWA because of the use of the extra log removals to address reliability. Can other measures be used to address this need, such as innovative or redundant monitoring and operational controls?

Chemical control. The requirements for ozone/biologically activated carbon before FAT is prescriptive and may inhibit innovation. Could performance goals be specified for the additional treatment?

Potential overlap in the programmes, plans, and reports. Could these requirements be a streamlined process to support efficient reporting and regulatory oversight?

Process to finalise DPR regulations

The SWB is currently working with an Expert Panel to review the proposed DPR criteria in the DPR Framework and Addendum. SWB requires that the Expert Panel make a determination that the criteria are protective of public health. As a result, the proposed criteria may be revised by SWB as part of the review process. The Expert Panel will complete its review in 2022 and SWB is on schedule to finalise the DPR criteria by December 2023. l

More information

SWRCB, 2018. A proposed framework for regulating direct potable reuse in California. State Water Resources Control Board. April 2018.

SWRCB, 2019. A proposed framework for regulating direct potable reuse in California. Second Edition, State Water Resources Control Board. August 2019.

SWRCB, 2021. DPR Framework 2nd edition Addendum – Early draft of anticipated criteria for direct potable reuse State Water Resources Control Board. 22 March 2021.

WRF, 2016. Potable Reuse Research Compilation: Synthesis of Findings. Water Research Foundation, Denver, CO.

The author

Jeff Mosher is General Manager, Santa Ana Watershed Project Authority, and a member of the IWA Water Reuse Specialist Group management committee.