Summary of California's Water Reuse Guideline or Regulation for 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, potable water reuse The 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. applications include indirect potable reuse (groundwater replenishment and reservoir water augmentation). The source of water treated municipal wastewater Treated 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 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 and pollutant discharges from a point source for surface water augmentation require a federal National Pollutant Discharge Elimination Systems (NPDES) permit (40 C.F.R. § 122). Additionally, potable water must meet California’s Safe Drinking Water Act regulations (SWRCB, 2021c). California indirect potable reuse regulations (IPR) require specific treatment requirements for certain pathogens and chemicals and projects must be reviewed and permitted on a site-specific basis by the Regional Water Board (Cal. Code Regs. tit. 22; SWRCB, 2018). Under California’s Water Quality Control Policy for Recycled Water (SWRCB, 2018), IPR via groundwater recharge requires a Waste Discharge Requirement permit.
Microbial (pathogen) log reduction values were derived assuming raw sewage maximum densities of 105 culturable enteric viruses/L, 105Giardia lamblia cysts/L and 104Cryptosporidium oocysts/L and a health-based target of less than 1 infection per 10,000 people per year. Risk-based calculations resulted in treatment requirements of a total of twelve-log enteric virus reduction, ten-log Giardia lamblia cyst reduction and ten-log Cryptosporidium oocyst reduction (i.e., 12/10/10 Rule). These reductions apply to potable reuse applications through groundwater injection and groundwater spreading. Reservoir water augmentation reuse applications must also meet specific dilution requirements, in addition to the groundwater injection reductions. Log reductions must be validated for each of the treatment processes used to meet the treatment requirements (Cal. Code Regs. tit. 22; CDPH, 2014).
For chemicals, California indirect potable reuse regulations include enhanced source control, treatment requirements and specific monitoring outcomes. Treatment must include reverse osmosis and advanced oxidation which is to provide a minimum of 0.5-log reduction of 1,4-dioxane (CDPH, 2014). Finished water must meet 0.5 mg/L total organic carbon (TOC) (CDPH, 2014) and monitoring requirements for constituents of emerging concern (CECs). Specific CECs that required to be monitored on a regular basis include health-based CECs that have been assigned Notification Levels (e.g., 1,4-dioxane, N-nitrosodimethylamine (NDMA), N-nitrosomorpholine (NMOR), perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA) and performance-based CECs (gemfibrozil, iohexol, sucralose, sulfamethoxazole) (SWRCB, 2018). Notification levels are health-based advisory levels established by the California’s Office of Environmental Health Hazard Assessment (OEHHA) that the State Water Board adopts for chemicals in drinking water that lack maximum contaminant levels (MCLs). When chemicals are found at concentrations greater than their notification levels, certain requirements and recommendations apply (SWRCB, 2021b). Additional CEC monitoring required by the Recycled Water Policy is an investigatory monitoring program recommended by a Science Advisory Panel to protect human health and the environment. The California Water Boards provides notification levels for chemicals (SWRCB, 2021b).
Types of planned potable reuse approved for use in California
Cal. Code Regs. tit. 22 defines the following approved potable uses:
- Indirect potable reuse (IPR)
- Groundwater replenishment: the planned use of recycled municipal wastewater that is operated for the purpose of replenishing a groundwater basin designated as a source of municipal and domestic water supply.
- Surface (spreading) application: the application of recharge water to a spreading area for infiltration resulting in the recharge of a groundwater basin or aquifer.
- Subsurface application: the application of recharge water to a groundwater basin(s) by a means other than surface application.
- Reservoir water augmentation: the planned use of recycled municipal wastewater into a surface water reservoir used as a source of domestic drinking water supply.
- Groundwater replenishment: the planned use of recycled municipal wastewater that is operated for the purpose of replenishing a groundwater basin designated as a source of municipal and domestic water supply.
Additional context and definitions
Surface spreading for groundwater augmentation applications are regulated via California’s Title 22 water reuse regulations (Cal. Code Regs. tit. 22). However, the treatment requirements differ for surface spreading applications compared to other indirect potable reuse applications. For surface spreading applications, tertiary treatment and disinfection (CT requirements of 450 mg/L*min) are required in addition to the soil aquifer treatment. Other indirect potable reuse applications, like groundwater injection and reservoir water augmentation, have advanced treatment requirements.
Potable reuse specifications
Summary of California's Potable Reuse Specifications
| Recycled Water Class/Category | Source Water Type | Water Quality Parameter* | Specification | Sampling/Monitoring Requirements (Frequency of monitoring; site/ location of sample; quantification methods) |
|---|---|---|---|---|
|
Groundwater replenishment– Surface application |
Municipal wastewater |
Viruses (enteric) |
12-log enteric virus reduction |
On-going monitoring |
|
Giardia lamblia |
10-log Giardia cyst reduction |
|||
|
Cryptosporidium |
10-log Cryptosporidium oocyst reduction |
|||
|
Retention time |
Minimum 2 months by added tracer Minimum 3 months by intrinsic tracer |
Verified by tracer |
||
|
Total nitrogen |
≤10 mg/L |
Two grab or 24-hour composite samples each week (at least 3 days apart) |
||
|
Inorganic chemicals listed in Table 64431-A (except for nitrogen compounds) |
≤ to MCLs or ALs specified in California's Drinking Water Regulations (SWRCB, 2021c) |
Quarterly grab or 24-hour composite samples |
||
|
Radionuclide chemicals listed in Tables 64442 and 64443 |
||||
|
Organic chemicals listed in Table 64444-A |
||||
|
Disinfection byproducts listed in Table 64533-A |
||||
|
Lead (Table 64678-A) |
||||
|
Copper (Table 64678-A) |
||||
|
Secondary drinking water contaminants in Tables 64449-A and 64449-B |
Annual grab or 24-hour composite sample |
|||
|
Total organic carbon (TOC) accounting for dilution, which is calculated via this equation TOC=0.5/RWC; RWC=Recycled Water Contribution or % of recycled water after mixing with diluent water |
TOC divided by the RMA RWC shall be ≤0.5 mg/L (20-week average) ≤0.5 mg/L (average of last four results) RMA= running monthly average |
Weekly 24-hour composite sample |
||
|
Health-based CECs |
≤ to NLs specified in California’s Drinking Water Notification Levels (SWRCB, 2021a) |
For each water recycling treatment plant, the recycled water producer shall conduct a three-phased monitoring approach for the CEC Monitoring Parameters, which includes an initial assessment monitoring phase (frequency=quarterly), followed by a baseline monitoring phase (frequency=semi-annually) and then a standard operation monitoring phase (frequency=semi-annually or annually).a |
||
|
Performance indicator CECs |
≤ to MTLs specified in Table 7 of California’s Recycled Water Policy (SWRCB, 2018) |
|||
|
Bioanalytical screening tools for CECs |
≤ to MTLs specified in Table 9 of California’s Recycled Water Policy (SWRCB, 2018) |
|||
|
Groundwater replenishment – Subsurface application |
Municipal wastewater |
Viruses (enteric) |
12-log enteric virus reduction |
On-going monitoring |
|
Giardia lamblia |
10-log Giardia cyst reduction |
|||
|
Cryptosporidium |
10-log Cryptosporidium oocyst reduction |
|||
|
Retention Time |
Minimum 2 months by added tracer Minimum 3 months by intrinsic tracer |
Verified by tracer |
||
|
Total nitrogen |
≤10 mg/L |
Two grab or 24-hour composite samples each week (at least 3 days apart) |
||
|
Inorganic chemicals listed in Table 64431-A (except for nitrogen compounds) |
≤ to MCLs or ALs specified in California's Drinking Water Regulations (SWRCB, 2021c) |
Quarterly grab or 24-hour composite samples |
||
|
Radionuclide chemicals listed in Tables 64442 and 64443 |
||||
|
Organic chemicals listed in Table 64444-A |
||||
|
Disinfection byproducts listed in Table 64533-A |
||||
|
Lead (Table 64678-A) |
||||
|
Copper (Table 64678-A) |
||||
|
Secondary drinking water contaminants in Tables 64449-A and 64449-B |
Annual grab or 24-hour composite sample |
|||
|
Total organic carbon |
≤0.5 mg/L (20-week average) ≤0.5 mg/L (average of last four results) |
Weekly 24-hour composite sample |
||
|
Health-based CECs |
≤ to NLs specified in California’s Drinking Water Notification Levels (SWRCB, 2021a) |
For each water recycling treatment plant, the “recycled water producer shall conduct a three-phased monitoring approach for the CEC Monitoring Parameters, which includes an initial assessment monitoring phase (frequency=quarterly), followed by a baseline monitoring phase (frequency=semi-annually) and then a standard operation monitoring phase (frequency=semi-annually or annually).”b |
||
|
Performance indicator CECs |
≤ to MTLs specified in Table 7 of California’s Recycled Water Policy (SWRCB, 2018) |
|||
|
Bioanalytical screening tools for CECs |
≤ to MTLs specified in Table 9 of California’s Recycled Water Policy (SWRCB, 2018) |
|||
|
Reservoir water augmentation |
Municipal wastewater |
Viruses (enteric) prior to a drinking water filtration plant |
Minimum 8 log enteric virus reductionc – based on available dilutiond |
On-going monitoring |
|
Giardia lamblia prior to a drinking water filtration plant |
Minimum 7 log Giardia cyst reductionc - based on available dilutiond |
|||
|
Cryptosporidium prior to a drinking water filtration plant |
Minimum 8 log Cryptosporidium oocyst reductionc based on available dilutiond |
|||
|
Minimum theoretical retention time |
Minimum 120 dayse |
Theoretical retention time (in units of days) = the volume of water in the surface water reservoir at the end of each month, divided by the total outflow from the surface water reservoir during the corresponding month |
||
|
Inorganic chemicals listed in Table 64431-A (except for nitrogen compounds) |
≤ to MCLs or ALs specified in California's Drinking Water Regulations (SWRCB, 2021c) |
Quarterly grab or 24-hour composite samples |
||
|
Radionuclide chemicals listed in Tables 64442 and 64443 |
||||
|
Organic chemicals listed in Table 64444-A |
||||
|
Disinfection byproducts listed in Table 64533-A |
||||
|
Lead (Table 64678-A) |
||||
|
Copper (Table 64678-A) |
||||
|
Secondary drinking water contaminants in Tables 64449-A and 64449-B |
Annual grab or 24-hour composite sample |
|||
|
Health-based CECs |
≤ to NLs specified in California’s Drinking Water Notification Levels (SWRCB, 2021a) |
For each water recycling treatment plant, the “recycled water producer shall conduct a three-phased monitoring approach for the CEC Monitoring Parameters, which includes an initial assessment monitoring phase (frequency=quarterly), followed by a baseline monitoring phase (frequency=semi-annually) and then a standard operation monitoring phase (frequency=semi-annually or annually).”b |
||
|
Performance indicator CECs |
≤ to MTLs specified in Table 7 of California’s Recycled Water Policy (SWRCB, 2018) |
|||
|
Bioanalytical screening tools for CECs |
≤ to MTLs specified in Table 9 of California’s Recycled Water Policy (SWRCB, 2018) |
Sources = SWRCB, 2018; Cal. Code Regs. tit. 22; and SWRCB 2021a.
CEC= chemicals of emerging concern; MTL= Monitoring trigger level; NL= notification level.
* Discharges to inland surface waters, enclosed bays and estuaries must also meet the Priority Toxic Pollutants criteria established in 40 C.F.R. § 131.
a Surrogates for the CECs for groundwater recharge - surface application include ammonia, dissolved organic carbon (DOC), nitrate, total fluorescence and UV light absorbance.
b Surrogates for the CECs for Reservoir water augmentation and groundwater recharge - subsurface application include electrical conductivity, DOC and UV light absorbance.
c It is assumed that additional pathogen reductions will occur through conventional drinking water treatment as follows: virus – 4 logs, Giardia lamblia – 3 logs and Cryptosporidium – 2 logs.
d The required reductions are as specified here if the volume of water withdrawn from the augmented reservoir to be ultimately supplied for human consumption contains no more than one percent, by volume, of recycled municipal wastewater that was delivered to the surface water reservoir during any 24-hour period. An additional log reduction via treatment for each pathogen class would be required if this constraint is not met and if the volume of water withdrawn from the augmented reservoir to be ultimately supplied for human consumption contains no more than ten percent, by volume, of recycled municipal wastewater that was delivered to the surface water reservoir during any 24-hour period.
e Minimum theoretical retention time is allowed down to 60 days provided an additional log reduction via treatment for each pathogen class is provided.
Upcoming state law or policy
Direct potable reuse (DPR): California has a 2023 deadline for adoption of raw water augmentation regulations. https://www.waterboards.ca.gov/drinking_water/certlic/drinkingwater/direct_potable_reuse.html
References:
2019 California Plumbing Code, Cal. Code Regs. tit. 24, § 5.
California Department of Public Health (CDPH). 2014. Groundwater Replenishment Reuse FINAL Regulations. Sacramento, CA.
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.
Potable Reuse, Cal. Assemb. B. Chapter 528, Cal. Stat. (2017).
Regulations Related to Recycled Water, Cal. Code Regs. tit. 22.
State Water Resources Control Board (SWRCB). 2018. Water Quality Control Policy for Recycled Water.
State Water Resources Control Board (SWRCB). 2021a. Drinking Water Notification Levels and Response Levels: An Overview.
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.
Please contact us at [email protected] 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.