California’s New Direct Potable Reuse Rules: What the Regulations Actually Require and Where Implementation Stands

What does California mean by direct potable reuse?

Recycled water going into a drinking water system without an environmental buffer. The rules define a DPR project as the planned introduction of recycled water either directly into a public water system or into a raw water supply immediately upstream of a water treatment plant.

That sets it apart from the rest of California's reuse spectrum:

• Non-potable reuse: recycled water in a separate purple pipe system for irrigation and industrial uses, under the Title 22 water recycling criteria. It never enters the drinking water supply.
• Indirect potable reuse: recycled water added to a groundwater basin or a reservoir, which acts as a buffer before the water is withdrawn and treated again.
• Direct potable reuse: no buffer. The safety margin that time and natural processes give in a basin or reservoir has to come from engineered treatment, monitoring and operations instead.

Was California the first state to adopt DPR rules?

No, Colorado was. Colorado's Water Quality Control Commission adopted a direct potable reuse rule into the state's primary drinking water regulations in fall 2022, which CDPHE announced as the first of its kind in the nation. California followed with its own, more prescriptive criteria, adopted in December 2023 to meet the December 31, 2023 deadline that the State Water Board's DPR background page traces to AB 574.

The two states' rules are not interchangeable. A project in California follows Title 22, and a project in Colorado follows Colorado's Regulation 11.

What treatment do the regulations actually require?

A train with separate barriers for pathogens and for chemicals, in a fixed order. The State Water Board's DPR regulation page links the final text. Section 64669.45, pathogen control, requires:

• validated log reductions that add up to at least 20 log for enteric virus, 14 log for Giardia cysts and 15 log for Cryptosporidium oocysts;
• at least four separate treatment processes for each pathogen, each credited with at least 1.0 log, and no single process credited with more than 6 log;
• at least three diverse mechanisms for each pathogen: a membrane physical separation, a chemical inactivation and a UV inactivation, unless an alternative is approved after independent advisory panel review.

Section 64669.50, chemical control, requires at least three processes in this sequence: ozone followed by biologically activated carbon, then reverse osmosis, then an advanced oxidation process. A continuous blending process with a municipal wastewater contribution of 0.10 or less can stand in for the ozone and BAC step.

What has to be in place besides treatment?

Much of the rule is about people, partners and paperwork. The responsible agency, called the DiPRRA, is a public water system, and the rules give it duties well beyond the plant:

• A joint plan (section 64669.20) with each partner agency, setting roles, legal authority and coordination over a 20-year planning horizon.
• Wastewater source control (section 64669.40). The wastewater agency must comply with its waste discharge requirements and run an industrial pretreatment and source control program with local limits and inspection authority.
• Operator certification (section 64669.35). A chief operator with a grade T5 water treatment certification over the whole train, and a shift operator with at least a T3 on every shift. The advanced treatment plant also needs operators holding advanced water treatment certificates: AWT5 for the chief, at least AWT3 for each shift.
• Plans and reports. An engineering report, an operations plan, a monitoring plan and a water safety plan, with pathogen and chemical control point monitoring and response.
• A public meeting held by the State Board before a permit or permit amendment can be issued (section 64669.25), and an independent advisory panel approved by the State Board reviews set items such as treatment alternatives, the water safety plan and the source control program (section 64669.120).

The source control piece is where industrial dischargers come in. If your facility sends process water to a sewer that feeds a DPR project, expect your POTW's pretreatment program to take a close interest in what you discharge.

Why is DPR a utility strategy and not a developer's shortcut?

Because the rules assume an agency with a drinking water permit, a treatment plant and a long horizon. Only a public water system can be the DiPRRA, and it needs partner wastewater agencies, a validated advanced treatment train and a certified operating staff around the clock.

A developer short on water for one project has other tools. Non-potable reuse under Title 22 is the usual one, through a recycled water purveyor and an engineering report. Our post on the Title 22 engineering report covers that step. DPR may later change what a regional agency can offer your project, but your own permits run through other frameworks.

Where does implementation stand in October 2026?

The rules are in force, and the work has moved to individual agencies. The rulemaking ended when the Office of Administrative Law approved the rules and filed them with the Secretary of State on August 6, 2024. The State Water Board's page marks the rulemaking complete.

Each project now has to work through its own validation studies, engineering report, environmental review, public meeting and permit. That is agency-by-agency work, measured in years of planning. If DPR matters to your supply, watch your regional water agency's plans and the Division of Drinking Water's DPR pages rather than the rule itself.

Limits of this article: it summarizes the adopted regulation text as published by the State Water Board, as of October 2026. It is general education, not a design basis. Any DPR project works from the full text and the Division of Drinking Water's review.

Frequently asked questions

When did California's DPR regulations take effect?

October 1, 2024. The State Water Board adopted them on December 19, 2023, and the Office of Administrative Law approved them on August 6, 2024.

Who can run a DPR project in California?

A public water system, acting as the direct potable reuse responsible agency, with a permit from the State Water Board and partner agencies for the wastewater supply.

What log reductions does California require for DPR?

At least 20 log for enteric virus, 14 log for Giardia cysts and 15 log for Cryptosporidium oocysts across the whole treatment train, from at least four separate processes for each pathogen.

I'm planning a large master-planned community in Southern California and water supply is tight. Can we build our own direct potable reuse plant for the project?

Not in any practical sense. The responsible agency must be a public water system with partner agencies, a joint plan, certified operators and a State Water Board permit. The realistic project-level options are non-potable recycled water through a purveyor and working with the local water agency on its supply plans.

I run a manufacturing plant that discharges to a sanitation district studying DPR. Will that change our pretreatment requirements?

It can. The DPR rules require the wastewater agency to run an industrial pretreatment and source control program that identifies and limits contaminants. Expect closer attention to chemicals of concern, and ask your POTW early how its plans may affect your permit.

Related resources

• How Texas Communities Are Solving Water Shortages with Direct Potable Reuse
• Understanding Order WQ 2016-0068-DDW: California's General Recycling Authorization
• Permitting Land Application: Choosing Between WDRs and Recycled Water Rules
• Water engineering in California

Sorting out which reuse path fits your water supply?

We help developers, utilities and municipalities match the reuse or discharge framework to the project's scale and schedule before engineering time goes to the wrong one. Tell us what you are weighing.

We specialize in:

• Water reuse and recycled water system planning
• Title 22 recycled water engineering reports
• Water supply and distribution engineering
• Wastewater treatment and pretreatment design
• Utility planning for municipalities and water agencies

Modern Engineering Solutions, McKinney, Texas. Contact: (214) 833-6748 or mod-eng.com