Summary of California's Water Reuse Guideline or Regulation for Agriculture

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
• History of microbial benchmarks in California
• History of key treatment requirements in California
• Water reuse for agriculture approved for use in California
• Water reuse treatment category for agriculture
• Additional context and definitions
• Water reuse for agriculture specifications (table)
• Upcoming state law or policy
• References
• Disclaimer

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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, water reuse for agriculture water reuse for agricultureThe use of recycled water for production of both crops for human consumption and non-food crops of commercial value. This reuse application excludes consumption by livestock, onsite non-potable reuse, and landscaping. includes surface irrigation of food crops, including all edible root crops where the recycled water comes into contact with the edible portion of the crop and where the edible portion is produced above the ground and not contacted by the recycled water; ornamental nursery stock and sod farms where access by the general public is not restricted; pasture for animals producing milk for human consumption; orchards where the recycled water does not come into contact with the edible portion of the crop; vineyards where the recycled water does not come into contact with the edible portion of the crop; non food-bearing trees; fodder and fiber crops; seed crops not eaten by humans; food crops that must undergo commercial pathogen-destroying processing before being consumed by humans; and ornamental nursery stock and sod farms provided no irrigation with recycled water occurs for a period of 14 days prior to harvesting, retail sale or allowing access by the general public. The source of water (treated municipal wastewater) 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 domestic 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

California allows the use of recycled municipal wastewater for agriculture, including surface irrigation of both food and non-food crops, animal pasture, orchards and vineyards and ornamental nursery stock (Cal. Code Regs. tit. 22). All applicable provisions of the Clean Water Act (CWA) (33 U.S.C. §§ 1251 et seq.), including its implementing regulations, must be met in addition to any relevant rule requirements under the Food Safety Modernization Act (FSMA) (124 Stat. 3885). California requires specific treatment for the reuse of reclaimed water for agriculture based on certain factors including the type of crop, use of the crop, post-harvest treatment of the crop and the potential for contact of the crop with the recycled water. 

Classes of recycled wastewater differ by both their treatment requirements and microbial specifications (Cal. Code Regs. tit. 22).

1. Undisinfected secondary recycled water requires no coliform standard.
2. Disinfected secondary-23 recycled water requires a 7-day median concentration of total coliform bacteria of ≤23 MPN/100 mL and must not exceed 240 MPN/100 mL in more than one sample in any 30-day period.
3. Disinfected secondary 2.2 recycled water requires that total coliform bacteria must not exceed 23 MPN/100 mL in more than one sample in any 30-day period and requires a 7-day median concentration of total coliform bacteria of ≤2.2 most probable number (MPN)/100 mL. 
4. Disinfected tertiary recycled water requires a 7-day median concentration of total coliform bacteria of ≤2.2 MPN/100 mL and requirement of ≤23 MPN/ 100 mL in more than one sample in any 30-day period. Additionally, it requires turbidity of ≤2 NTU in the filter effluent and a 5-log removal of F-specific bacteriophage MS-2 or poliovirus.

History of microbial benchmarks in California

1. Total coliform standard of 2.2 most probable number (MPN)/100 mL represents the non-detect threshold in a standard MPN test and is not based on a formal risk assessment, but rather on experience and the knowledge that accepted treatment processes can effectively reduce pathogen numbers (National Research Council, 1996). Historically, a concentration of total coliform bacteria of ≤2.2 MPN/100 mL served as the drinking water standard in California (NWRI, 2012). Drinking water meeting this criterion was categorized as “pathogen free” in the absence of quantification methods for viruses (NWRI, 2012).
2. Total coliform standard of 23 MPN/100 mL was established in 1968 as an indicator that a disinfection process was operating effectively for oxidized (but not filtered) wastewater. 
3. Total coliform standard of 240 MPN/100 mL was established in 1978 to assure a robust disinfection process and avoid brief lapses in treatment. 
4. The 5-log reduction in virus requirement is based on a correlation to a total coliform reduction to ≤ 2.2 MPN/100 mL in Pomona’s tertiary effluent. The 1977 Pomona Virus Study evaluated a range of operational treatment conditions across pilot treatment trains using seeded poliovirus I (Sanitation Districts of Los Angeles County, 1977). The CT requirement specified in the Water Recycling Criteria (NWRI, 2012) of 450 mg-min/L is based on the Pomona Virus Study, which used combined chlorine and a modal contact time of about 90 minutes. The study determined a CT of 450 mg-min/L met the coliform standard of 2.2 MPN/100 mL and simultaneously reduced the seeded virus level by 5-logs.  

History of key treatment requirements in California

In addition to the above microbial water quality standards, the treatment for the highest end uses involving food crop and landscape irrigation were based on drinking water standards because the exposures were considered similar. The degree of treatment and levels of disinfection specified are commensurate with the expected level of public exposure to the treated wastewater. 

1. Oxidation of wastewater is required to assure an acceptable minimal quality of recycled water and to have a recycled water that is more uniform in quality than primary effluent and with a lower ammonia and organic content to assure reliable disinfection of the water (NWRI, 2012).
2. Coagulation is required based on studies carried out by the US Public Health Service at the Robert A. Taft Sanitary Engineering Center, which demonstrated that the use of chemical coagulants with media filtration is the most effective and practical method of removing viruses and suspended material that may contain viruses from the water being treated (NWRI, 2012).
3. Filtration is necessary to assure physical removal of the agglomerated material which may contain virus particles and other particulates that could shield virus from disinfectants in the recycled water. A turbidity limit of 10 NTU was originally established in 1968 to assure the filtration process is functioning properly (NWRI, 2012.) The turbidity limit was lowered in 1975 (average of 2 NTU and not to exceed 5 NTU more than 5 percent of the time during any 24-hour period) to assure that the filtration process produces a water quality that enables the downstream disinfection process to be effective and reliable. Subsequent adjustments of the turbidity standard were made to establish achievable limits, taking into account the capabilities of a filtration technology and requirements of the disinfection process. Specific maximum turbidity limits were established in 2000 to assure that filters would not be operated at the high rates which result in breakthrough of solids (NWRI, 2012.)
4. Chlorine disinfection: The regulations require a minimum chlorine concentration versus time (generally referred to as CT values) of 450 based on a minimum 90-minute contact time. These requirements are based on the Department of Public Health’s (Department, now DDW) experience with several demonstration projects (including the 1977 report on the Pomona Virus Study) where these concentrations and detention times were shown to be effective in inactivating viruses and on operational testing data submitted by the Los Angeles County Sanitation Districts (Sanitation Districts of Los Angeles County, 1977). Based on these data, CDPH published a policy statement (Policy Statement for Wastewater Reclamation Plants with Direct Filtration) that required a chlorine residual of at least 5 mg/L after a modal contact time of at least 90 minutes (NWRI, 2012), which resulted in a minimum allowable CT of 450 mg-min/L. The CT and modal contact time requirements were incorporated into the 2000 revision of the 1978 criteria, which as originally only based on coliform inactivation (NWRI, 2012).
5. Alternative disinfection: The regulations also allow an alternative disinfection method if it is demonstrated to be capable of removing or inactivating viruses to a level of 1/100,000 (5 logs) of the initial concentration. The demonstration of a 5-log reduction or use of the specified CT values were determined by the Department to be necessary to assure effective and reliable removal and inactivation of enteric viruses for those uses where the public exposure to the recycled water is high (NWRI, 2012).

Water reuse for agriculture approved for use in California

Cal. Code Regs. tit. 22 defines the following approved water reuse for agriculture, which consists of surface irrigation of:

• Food crops, including all edible root crops, where the recycled water comes into contact with the edible portion of the crop (Disinfected Tertiary)
  • No recycled water used for irrigation, or soil that has been irrigated with recycled water, shall come into contact with the edible portion of food crops eaten raw by humans unless the recycled water is categorized as Disinfected Tertiary
• Food crops where the edible portion is produced above ground and not contacted by the recycled water (Disinfected Secondary-2.2)
• Ornamental nursery stock and sod farms where access by the general public is not restricted (Disinfected Secondary-23)
• Pasture for animals producing milk for human consumption (Disinfected Secondary-23)
• Orchards where the recycled water does not come into contact with the edible portion of the crop (Undisinfected Secondary)
• Vineyards where the recycled water does not come into contact with the edible portion of the crop (Undisinfected Secondary)
• Non food-bearing trees (including Christmas tree farms, provided no irrigation with recycled water occurs for a period of 14 days prior to harvesting or allowing access by the general public) (Undisinfected Secondary)
• Fodder and fiber crops (Undisinfected Secondary) 
• Seed crops not eaten by humans (Undisinfected Secondary)
• Food crops that must undergo commercial pathogen-destroying processing before being consumed by humans (Undisinfected Secondary)
• Ornamental nursery stock and sod farms provided no irrigation with recycled water occurs for a period of 14 days prior to harvesting, retail sale, or allowing access by the general public (Undisinfected Secondary)

Water reuse treatment category for agriculture

In California, the various classes of recycled water treatment are defined by their respective treatment requirements and applicable performance standards. The respective treatment requirements are briefly summarized regarding water reuse for agriculture:

• For disinfected tertiary recycled water, the treatment requirements are filtration and disinfection via chlorine disinfection or another disinfection process, that when combined with filtration, achieves a 5-log inactivation or removal of plaque forming units of F-specific bacteriophage MS-2, poliovirus, or a similar virus. In the disinfected effluent, the median concentration of total coliforms cannot exceed 2.2 MPN/100 mL (based on a median concentration using results of the last 7 days for which analyses have been completed), cannot exceed 23 MPN/100 mL in more than one sample in any 30-day period and cannot exceed 240 MPN/100 mL in a single sample. A disinfected tertiary recycled water can also be a chlorine disinfection process following filtration that provides a CT value of not less than 450 mg-min/L at all times with a modal contact time of at least 90 minutes based on peak dry weather design flow.
• For disinfected secondary-2.2 recycled water, the treatment requirements are secondary treatment with oxidation and disinfection. The water must meet a 7-day median concentration of ≤2.2 MPN/100 mL of total coliform bacteria with a 30-day median concentration of ≤23 MPN/100 mL.
• For disinfected secondary-23 recycled water, the treatment requirements are oxidation and disinfection and water must meet a 7-day median concentration of ≤23 MPN/100 mL of total coliform bacteria. Total coliform must not exceed 240 MPN/100 mL in more than one sample in any 30-day period.
• For undisinfected secondary recycled water, the treatment requirements are secondary treatment with oxidation.

Additional context and definitions

In California, recycled municipal wastewater is defined as “recycled water that is the effluent from the treatment of wastewater of municipal origin” (Cal. Code Regs. tit. 22).

All use areas where recycled municipal wastewater is used that are accessible to the public must have signs posted that include the wording “RECYCLED WATER – DO NOT DRINK” and display the international “Do Not Drink” symbol (Cal. Code Regs. tit. 22). No physical connection is allowed to exist between a recycled water system and a potable water system (except as allowed under Section 7604 of Title 17). The portions of the recycled water in areas accessed by the general public (except for cemeteries) must not include any hose bibs and must use quick couplers that differ from those used on the potable water system. 

Water reuse for agriculture specifications

Summary of California's Water Reuse for Agriculture Reuse Specifications

Source= Cal. Code Regs. tit. 22

* Information about sampling and monitoring requirements such as frequency, site and quantification methods not specifically listed in the table was not explicitly specified in the state-specific regulations.

^a The CT is the product of total chlorine residual and modal contact time measured at the same point (Cal. Code Regs. tit. 22). This only applies if chlorine was used for disinfection. 

^b This only applies if a disinfection process other than chlorination was used.

^c A virus that is at least as resistant to disinfection as polio virus may be used for the purposes of the demonstration.

^d The Regional Boards may include the nitrogen and phosphorous limits or control for the protection of beneficial uses, or as required by Basin Plans.

Upcoming state law or policy

No upcoming regulations pertaining to water reuse for agriculture were found for California.

References

Clean Water Act, 33 U.S.C. §§ 1251 et seq.

Food Safety Modernization Act (FSMA), 124 Stat. 3885.

National Research Council (NRC). 1996. Use of Reclaimed Water and Sludge in Food Crop Production, National Academy Press, Washington, D.C.

National Water Research Institute (NWRI). 2012. Review of California’s Water Recycling Criteria for Agricultural Irrigation.

Sanitation Districts of Los Angeles County. 1977. Pomona Virus Study - Final Report. Report prepared by Sanitation Districts of Los Angeles County for California State Water Resources Control Board, Sacramento, CA.

Water Recycling Criteria, Cal. Code Regs. tit. 22.

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Disclaimers

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