Summary of California’s Water Reuse Guideline or Regulation for Direct Potable Water Reuse

This page is part of the EPA’s REUSExplorer tool, which summarizes the different state level regulations or guidelines for water reuse for a variety of sources and end-uses.
The source water for this summary is Treated Municipal Wastewater.

• Technical basis
• Types of planned potable reuse approved for use in California
• Additional context and definitions
• Potable reuse specifications (table)
• Upcoming state law or policy
• References
• Disclaimer

This page is a summary of the state's water reuse law or policy and is provided for informational purposes only. Please always refer to the state for the most accurate and updated information.

In California, direct potable water reusedirect potable water reuseThe use of highly treated recycled water for drinking water purposes. This reuse application includes both indirect potable reuse through introduction of recycled water into an environmental buffer such as a surface reservoir or groundwater aquifer, and direct potable reuse through introduction of recycled water into a drinking water system. augmentation directly into a public drinking water system or into a raw water supply immediately upstream of a drinking water treatment plant. The source of water (treated municipal wastewatertreated municipal wastewaterTreated wastewater effluent discharged from a centralized wastewater treatment plant of any size. Other terms referring to this source of water include domestic wastewater, treated wastewater effluent, reclaimed water, and treated sewage.) is specified by the state as municipal wastewater. The write-up uses state terms when discussing sources or uses of water that may differ from the Regulations and End-Use Specifications Explorer's (REUSExplorer's) terms.

Technical basis

Potable water supplied by a public water system in the United States must meet all applicable Safe Drinking Water Act (SDWA) requirements, including its implementing regulations (40 C.F.R. § 141) for chemical and microbial contaminants. Additionally, potable water must meet California's Safe Drinking Water Act regulations (SWRCB, 2021c). California direct potable reuse (DPR) regulations require that municipal wastewater for use in DPR projects be supplied by facilities operating an industrial pretreatment and pollutant source control program and being regulated via a waste discharge permit (Cal. Code Regs. Tit. 22, § 64669). The full flow entering a wastewater treatment works may not be accepted by a DPR facility (e.g., a DPR facility may be offline for routine maintenance or addressing compliance issues) and wastewater should be able to be diverted to another existing discharge location(s) upstream of the DPR facility. Prior to entry into a public water distribution system, municipal wastewater for DPR is required to be treated for certain pathogens and chemicals which are summarized in the Summary of California's Potable Reuse Specifications table.

California also requires a domestic water supply permit or amended domestic water supply permit prior to the operation of a DPR project (Cal. Code Regs. tit. 22, § 64669.15(c)). The DiPRRA, or direct potable reuse responsible agency, is the public water system responsible for compliance with the regulation for a DPR project. The DiPRRA must submit a permit application for the DPR project that includes: an engineering report (§ 64669.75); joint plan describing partner agency coordination procedures (§ 64669.20); demonstration of technical, managerial, and financial capacity (§ 64669.30); an operations plan (§ 64669.80); and a monitoring plan (§ 64669.90). A DiPRRA must provide information (e.g., a description of the DPR project, municipal wastewater source(s), treatment processes, etc) for at least one public meeting held by the State Water Board before a permit can be issued for the DPR project (§ 64669.25).

In California, for the treatment train to reliably provide microbiologically safe drinking water, the treatment train must have multiple, independent treatment barriers (i.e., redundancy) and be designed to include extra log reduction capacity beyond the required log reductions. California derived microbial (pathogen) log reduction targets (LRTs) for direct potable water reuse in three steps (SWRCB, 2021d):

1. The first step involved taking the highest organism density that could be expected in raw municipal sewage and calculating the reduction necessary to achieve the allowable density in drinking water, a total of sixteen-log enteric virus reduction, ten-log Giardia lamblia cyst reduction, and eleven-log Cryptosporidium oocyst reduction (i.e., 16/10/11) between raw wastewater and finished drinking water.
   • The allowable density in drinking water was calculated to limit the annual risk of infection to less than 1 infection in 10,000 people per year (SWRCB, 2021d).  
   • LRTs were derived assuming raw sewage maximum densities of 10⁹ norovirus gene copies/L, 10⁵ Giardia cysts/L and 10⁴ Cryptosporidium oocysts/L (SWRCB, 2021d).  
2. The second step involved the probabilistic analysis of treatment train performance using a conservative critical treatment failure scenario to generate the excess log capacity needed to achieve an annual risk of infection that does not exceed 1 infection in 10,000 people per year: four-log enteric virus reduction, four-log Giardia lamblia cyst reduction, and four-log Cryptosporidium oocyst reduction (e.g., 4/4/4).
3. The two derivations (16/10/11 and 4/4/4) were then added together for a total overall required LRT of twenty-log enteric virus reduction, fourteen-log Giardia lamblia cyst reduction, and fifteen-log Cryptosporidium oocyst reduction (i.e., 20/14/15).

Further details on the derivation of LRTs can be found in SWRCB (2021d).

The treatment train must consist of no less than four separate treatment processes for the reduction of enteric viruses, Giardia cysts, and Cryptosporidium oocysts. At least four of the treatment processes must be credited with at least a 1.0 log reduction, and no single process may be credited with more than 6 log reduction (Cal. Code Regs. tit. 22, § 64669.45(a)(2)). A single treatment process may receive pathogen log reduction credits for one or more pathogens. At least three diverse treatment mechanisms must be used in the treatment train, including one membrane physical separation mechanism, one chemical inactivation mechanism, and one UV inactivation mechanism. An alternative mechanism for a treatment mechanism may be approved if it meets several additional requirements (see § 64669.45(a)(3)). Log reductions must be validated for each of the treatment processes used to meet the treatment requirements (Cal. Code Regs. tit. 22, § 64669.45(a)(4)).

For chemicals, California DPR regulations include industrial pretreatment and pollutant source control, treatment requirements, and specific monitoring outcomes. Treatment must consist of an ozonation process paired with biologically activated carbon (BAC), a reverse osmosis membrane process, and advanced oxidation in the listed order (Cal. Code Regs. tit. 22, § 64669.50(a) and (b)). The ozone/BAC process should provide at least a one-log reduction of indicator chemicals formaldehyde, acetone, carbamazepine, and sulfamethoxazole. A continuous blending process that provides a municipal wastewater contribution (WWC) of ≤10% may be substituted for an ozone/BAC process. The reverse osmosis membrane regulates total organic carbon (TOC) concentrations, among other factors, and must meet certain design performance targets based on rejection of sodium chlorine and total organic carbon, in addition to continuously monitored surrogate(s) that indicate when the integrity of the RO membrane is compromised. Advanced oxidation must provide a minimum 0.5-log reduction of 1,4-dioxane. Finished water of wastewater origin must be no greater than 0.5 mg/L TOC before entry into the drinking water distribution system. Monthly sampling is further required for chemicals specified by the State Water Board based on a review of the DPR project engineering report, including: chemicals with a primary or secondary MCL or action level; priority toxic pollutants (40 C.F.R. § 131.38); chemicals with Notification Levels; solvents (e.g., acetone; N,N-demethylacetamide; methanol; and methyl ethyl ketone); treatment byproduct precursors and treatment byproducts; chemicals associated with business or household sources of hazardous substances, pharmaceuticals, and personal care products; and any other chemicals specified by the State Water Board that may pose a human health risk (Cal. Code Regs. tit. 22, § 64669.60 and 64669.65).

Types of planned direct potable reuse approved for use in California

Cal. Code Regs. tit. 22, § 64669.05 defines the following approved DPR applications:

• Direct potable reuse: the planned introduction of recycled municipal wastewater either directly into a public water system or into a raw water supply immediately upstream of a water treatment plant.

A summary of California's indirect potable reuse applications can be found in the Summary of California's Water Reuse Guideline or Regulation for Indirect Potable Water Reuse.

Additional context and definitions

The California DPR regulation is applicable to a public water system that uses municipal wastewater to produce water to augment a source of supply for a public water system's drinking water treatment plant or placed into a public water system's drinking water distribution system (Cal. Code Regs. tit. 22 § 64669.00).

In California, the benefit of continuous blending of DPR project water with another approved source of water (e.g., extracted groundwater source or a surface water source of drinking water) may be substituted for up to two logs of the pathogen log reduction requirements (Cal. Code Regs. tit. 22 § 64669.45(d)(1)). If a reservoir is present in a project, mixing with water in a reservoir could also offset up to 2 logs for a limited duration of up to 60 minutes in any 24-hour period, if the conditions in Cal. Code Regs. tit. 22 § 64669.45(d)(2) are met. Mixing is fundamentally different than the two other options 8-=to offset no more than 2 logs of the pathogen reduction criteria, calculated using 0.033 logs per day times the retention time (in days).

The DPR project treatment train must also be designed to meet the chemical treatment requirements and must be comprised of not less than three separate treatment processes (with three diverse treatment mechanisms) for chemical reduction (Cal. Code Regs. tit. 22). The DiPRRA must submit a report (containing monitoring results, corrective actions, process failures that occurred, etc.) for each treatment train process to the State Water Board after the first 12 months of full-scale operation. This report is intended for reporting of information about treatment efficacy, monitoring and treatment issues and/or failure, and what was (or will be done) to address those issues. If there is any treatment process not operating in compliance with its associated critical limits more than 10% of the time the treatment train was producing water in a calendar month, an evaluation and corrective actions are required, with a summary provided in the monthly compliance report.

• Ozone/BAC process: must be designed to provide a ratio of the applied ozone dose to the design feed water TOC concentration >1.0 and an empty bed contact time of at least 15 minutes. A different ratio and/or empty bed contact time may be used if it can be demonstrated that the alternative ratio and/or empty bed contact time can achieve the reduction of the indicators specified (Cal. Code Regs. tit. 22 § 64669.50(d)).
• Reverse osmosis membrane: must achieve a minimum rejection of sodium chloride ≥99% and an average rejection of sodium chloride ≥99.2%. During the first 20 weeks of operation, the membrane must produce a permeate with no more than 5% of sample results with a TOC >0.25mg/L through monitoring no less frequent than weekly. During full-scale operation, the DiPRRA must continuously monitor and record the surrogate and/or operational parameter(s) that indicate when the integrity of the reverse osmosis process has been compromised and when critical limits have been exceeded. The TOC performance must be tracked, and corrective action must be taken if the TOC exceeds certain levels during certain time frames, as specified in § 64669.50 (j)(1) and (j)(2).
• Advanced oxidation process: must be designed and validated to reliably provide ≥ 0.5 log reduction of the indicator 1,4-dioxane.

The DiPRRA must establish a TOC chemical control point and monitoring location that provides a representative sampling of the advanced water treatment prior to distribution. TOC must be monitored continuously and recorded no less than once every 15 minutes (Cal. Code Regs. tit. 22 § 64669.50(n)). When DPR project water is being blended prior to distribution with an untreated source of water or a finished water previously approved by the State Water Board, the TOC concentration must not exceed a TOC critical limit ≤ 0.5 mg/L divided by the WWC. The TOC critical limit must always be based on the current WWC).

Additional details on the following topics can be found within the following regulation sections:

• Pathogen control (§ 64669.45)
• Chemical control (§ 64669.50)
• Regulated Chemicals and Physical Characteristics Control and Monitoring (§ 64669.60)
• Additional chemical monitoring (§ 64669.65)
• Laboratory analysis (§ 64669.70)
• General requirements (§ 64669.10)
• Permitting (§ 64669.15)
• Joint plan with partner agency coordination (§ 64669.20)
• Public meeting (§ 64669.25)
• Technical, managerial, and financial capacity (§ 64669.30)
• Operator certification (§ 64669.35)
• Wastewater source control (§ 64669.40)
• Water safety plan (§ 64669.55)
• Engineering report (§ 64669.75)
• Operations plan (§ 64669.80)
• Pathogen and Chemical Control Point Monitoring and Response (§ 64669.85)
• Monitoring plan (§ 64669.90)
• Compliance reporting (§ 64669.95)
• Annual report (§ 64669.100)
• Cross-connection control (§ 64669.105)
• Corrosion control (§ 64669.110)
• Independent advisory panel (§ 64669.120)
• Public notification (§ 64669.125)
• Consumer confidence report (§ 64669.130)

Potable reuse specifications

Summary of California's Direct Potable Reuse Specifications

Sources = Cal. Code Regs. tit. 22, § 64669

AL= action level; AOP= advanced oxidation process; CEC= chemicals of emerging concern; DiPRRA= Direct potable reuse responsible agency; MCL=maximum contaminant level; MTL= Monitoring trigger level; NL= notification level.

^a If the SCADA system detects a failure of a process to meet the 16/10/11 LRVs, it must automatically discontinue delivery of DPR project water to any distribution point.

^b The monitoring frequency may be increased for a chemical based on the State Water Board's review of the DPR project engineering report and evaluation of the treatment process used, the treatment effectiveness, and the concentration of the chemical found in the feed water source.

^c The State Water Board may require representative monitoring at additional locations based on their review of the DPR project engineering report.

^d Or at an alternative location approved by the State Water Board.

^e Monitoring conducted at this location may be used to satisfy the monitoring requirement at the location immediately after the AOP if the DiPRRA demonstrates to the State Water Board that the water sampled at these locations have the same or substantially similar water quality.

^f The critical limits established for the nitrate and nitrite chemical control point shall not be greater than the respective MCLs for nitrate, nitrite, or nitrate plus nitrite.

^g The monthly sample collected at this location may be used to satisfy the weekly sampling requirement when the sample date of the monthly sample and the sample date of the weekly sample coincide.

^h The DiPRRA may apply to the State Water Board to have the monitoring frequency decreased for a chemical that meets the criteria in § 64669.65(f).

Upcoming state law or policy

No upcoming regulations pertaining to direct potable reuse were found for California.

References

2019 California Plumbing Code, Cal. Code Regs. tit. 24, § 5.

Direct Potable Reuse (pdf), Cal. Code Regs. tit. 22, § 64669.

EPA-Administered Permit Programs: The National Pollutant Discharge Elimination System, 40 C.F.R. § 122.

National Primary Drinking Water Regulations, 40 C.F.R. § 141.

Regulations Related to Recycled Water (pdf), Cal. Code Regs. tit. 22, § 60320.

Secondary Maximum Contaminant Levels and Compliance (pdf), Cal. Code Regs. tit. 22, § 64449.

State Water Resources Control Board (SWRCB). 2021a. Drinking Water Notification Levels and Response Levels: An Overview (pdf)

State Water Resources Control Board (SWRCB). 2021b. Drinking Water Notification Levels.

State Water Resources Control Board (SWRCB). 2021c. California Safe Drinking Water Laws: Selected Provisions of the Health & Safety Code and Water Code (pdf).

State Water Resources Control Board (SWRCB). 2021d. LRV Derivation (ca.gov) (pdf)

Disclaimers

Please contact us at waterreuse@epa.gov if the information on this page needs updating or if this state is updating or planning to update its laws and policies and we have not included that information on the news page.