2.1 California Title 22 Recycled Water Standards

California Title 22 Recycled Water Standards

Water recycling is a cornerstone of California's long-term water resilience strategy. The primary legal framework governing the production, distribution, and use of non-potable and potable recycled water in California is codified in the California Code of Regulations (CCR) Title 22, Division 4, Chapter 3 (known comprehensively as the Water Recycling Criteria). Enacted to safeguard public health while encouraging resource recovery, Title 22 establishes strict biological, chemical, and operational benchmarks that every certified water and wastewater treatment operator must master.

Regulatory authority is shared between two key state bodies:

1. State Water Resources Control Board (SWRCB) Division of Drinking Water (DDW): Formulates health-protective criteria, establishes statutory water quality standards, reviews engineering reports, and approves treatment technologies.
2. Regional Water Quality Control Boards (RWQCBs): Issues enforceable permits—including Water Reclamation Requirements (WRRs), Waste Discharge Requirements (WDRs), and Master Recycling Permits—that mandate ongoing operational compliance and water quality monitoring.

Before any recycled water project can deliver water to end users, the producer and distributor must submit a comprehensive Title 22 Engineering Report (CCR Title 22 § 60323) to DDW and the appropriate Regional Board detailing treatment processes, reliability features, alarm setpoints, and emergency diversion protocols.

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The Four Title 22 Recycled Water Quality Classifications

Title 22 categorizes recycled water into four distinct tiers based on the degree of secondary biological oxidation, filtration, and chemical or physical disinfection achieved. As potential human contact and exposure increase, the regulatory treatment standards become progressively more stringent.

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Disinfected Tertiary Recycled Water: Technical Deep-Dive

Disinfected tertiary recycled water represents the highest standard for non-potable reuse and requires dual barriers: advanced filtration followed by high-level disinfection.

1. Filtration Standards & Turbidity Limits

Filtration removes particulate matter, suspended solids, and parasite cysts (such as Giardia and Cryptosporidium), ensuring that downstream disinfectants can penetrate remaining microorganisms without shielding.

• Conventional Granular Media Filtration (Rapid sand, dual-media anthracite/sand, or multi-media):
  • Daily 24-hour average turbidity must not exceed 2 NTU (Nephelometric Turbidity Units).
  • Turbidity must not exceed 5 NTU for more than 5 percent of the time during any 24-hour period.
  • Turbidity must never exceed 10 NTU at any instantaneous moment.
• Membrane Filtration (Microfiltration [MF] or Ultrafiltration [UF]):
  • Turbidity must not exceed 0.2 NTU for more than 5 percent of the time within any 24-hour period.
  • Turbidity must never exceed 0.5 NTU at any time.

Operational Directive: If tertiary effluent turbidity exceeds regulatory limits, automated plant controls must immediately divert the off-spec water back to the plant headworks or equalization basins. Unfiltered or improperly filtered water must never reach the disinfection contact basin.

2. Disinfection Kinetics and the CT Standard

Title 22 mandates strict disinfection performance criteria for disinfected tertiary water to ensure near-complete viral and bacterial inactivation:

• Chlorine Contact Kinetics ($CT$ Concept): $\text{CT} = C \times T_{10} \ge 450\text{ mg}\cdot\text{min}/\text{L}$ Where:
  • $C$ is the modal chlorine residual (in $\text{mg/L}$) measured at the end of the contact chamber.
  • $T_{10}$ is the modal contact time (in minutes) through the chamber under peak dry-weather or wet-weather hourly flow rates.
  • Title 22 requires a minimum modal contact time of not less than 90 minutes at peak design flow.
• Alternative Disinfection (Ultraviolet / UV):
  • Facilities utilizing UV disinfection instead of chlorine must demonstrate an inactivation credit equivalent to chlorine disinfection. The National Water Research Institute (NWRI) guidelines, incorporated into Title 22 approvals, require UV systems to achieve at least 5-log inactivation of virus (using MS2 or poliovirus surrogates), typically requiring an applied design dose of >= 100 mJ/cm².

3. Bacteriological Sampling Standards

Samples must be collected daily at the effluent compliance point:

• 7-Day Median Total Coliform: Must not exceed 2.2 MPN / 100 mL (Most Probable Number per 100 milliliters).
• 30-Day Ceiling: Must not exceed 23 MPN / 100 mL in more than one sample in any 30-day rolling window.
• Instantaneous Maximum: Must never exceed 240 MPN / 100 mL in any single grab sample.

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Secondary Recycled Water Tiers & Specific Uses

Disinfected Secondary-2.2

Disinfected Secondary-2.2 utilizes biological oxidation and disinfection without tertiary filtration. Total coliform limits match the 7-day median of tertiary water (<= 2.2 MPN/100 mL, max single sample <= 23 MPN/100 mL in 30 days). Permitted uses include:

• Surface irrigation of food crops where the edible portion of the crop grows entirely above ground and receives no direct contact with recycled water (e.g., drip-irrigated citrus orchards, avocado groves, and trellised wine vineyards).
• Restricted access landscape irrigation, such as freeway medians and interchange landscaping.

Disinfected Secondary-23

Disinfected Secondary-23 requires biological oxidation and moderate disinfection (7-day median <= 23 MPN/100 mL; max single sample <= 240 MPN/100 mL in 30 days). Permitted uses include:

• Irrigation of pasture grazed by milking animals (dairy cattle, goats).
• Industrial cooling towers operating without mist-producing draft equipment.
• Landscape impoundments without body contact.
• Construction water for soil compaction, dust suppression, and concrete batching.

Undisinfected Secondary

Undisinfected secondary water is oxidized secondary effluent that has received no pathogen disinfection. Permitted uses are strictly non-contact:

• Irrigation of non-food vegetation, including silviculture (tree farms), fiber crops (cotton), and seed crops.
• Pasture grazed exclusively by non-milking livestock (beef cattle).

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Direct Potable Reuse (DPR) Regulations (2023/2024 Framework)

In December 2023 (formally codified in 2024), the SWRCB adopted landmark regulations for Direct Potable Reuse (DPR), establishing rules for introducing purified recycled water directly into a public drinking water distribution system or raw water conveyance upstream of a drinking water treatment plant without an environmental buffer (such as an aquifer or reservoir).

+---------------------------------------------------------------------------------------------------------+
|                               DIRECT POTABLE REUSE (DPR) TREATMENT TRAIN                               |
+---------------------------------------------------------------------------------------------------------+
|  [Secondary BNR Effluent]                                                                               |
|           |                                                                                             |
|           v                                                                                             |
|  [Microfiltration / Ultrafiltration (MF/UF)]   ==> Target: Giardia/Cryptosporidium (>= 4-log removal)   |
|           |                                                                                             |
|           v                                                                                             |
|  [Reverse Osmosis (RO)]                        ==> Target: Salts, PFAS, TOC, Viruses (>= 1.5-2 log)     |
|           |                                                                                             |
|           v                                                                                             |
|  [Advanced Oxidation Process (UV/AOP)]         ==> Target: NDMA, 1,4-Dioxane, Pathogens (>= 6-log virus)|
|           |                                                                                             |
|           v                                                                                             |
|  [Granular Activated Carbon / Free Chlorine]   ==> Target: Disinfection byproducts, Residual stability  |
|           |                                                                                             |
|           v                                                                                             |
|  [Engineered Storage Buffer (ESB)]             ==> Target: Real-time verification & emergency diversion |
|           |                                                                                             |
|           v                                                                                             |
|  [Finished Potable Drinking Water Distribution]                                                         |
+---------------------------------------------------------------------------------------------------------+

The 12-10-10 Pathogen Log Reduction Standard

DPR facilities must achieve unprecedented multi-barrier pathogen removal between raw wastewater influent and finished purified water:

• Enteric Virus: 12-log reduction ($99.9999999999%$ removal/inactivation).
• Cryptosporidium oocysts: 10-log reduction ($99.99999999%$ removal/inactivation).
• Giardia duodenalis cysts: 10-log reduction ($99.99999999%$ removal/inactivation).

Multi-Barrier Treatment & Capping Mandates

To guarantee fail-safe operation, DDW established strict structural engineering requirements:

1. Barrier Independence: At least three separate, independent treatment processes must be deployed for each target pathogen class (virus, Cryptosporidium, and Giardia).
2. Log Credit Capping: No single treatment process can be credited with more than 6-log reduction toward any pathogen category, preventing over-reliance on a single mechanism.
3. Continuous Critical Control Point (CCP) Monitoring: Every barrier must be monitored continuously online using validated surrogates (e.g., pressure decay tests for MF/UF, electrical conductivity / TOC reduction for RO, and UV sensor intensity/transmittance for UV-AOP). Any excursion triggers immediate, automatic diversion of off-spec water to the sewer system before it reaches the engineered storage buffer.

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Cross-Connection Control & Physical Site Protection

To prevent catastrophic cross-contamination between recycled water and potable drinking water distribution networks, California enforces rigorous physical isolation rules:

• Color Coding: All recycled water transmission mains, distribution piping, valves, sprinkler risers, and valve boxes must be colored Pantone 512 Purple or wrapped in purple polyethylene warning tape.
• Signage: Warning signs displaying the international "Do Not Drink" symbol and text in English and Spanish ("CAUTION: RECYCLED WATER – DO NOT DRINK") must be posted at all reuse sites.
• Separation Distances: Recycled water pipelines must maintain a minimum 10-foot horizontal separation from parallel potable water mains and be installed at least 1 foot below potable lines in vertical crossings.
• Setback from Potable Wells: Disinfected tertiary irrigation must maintain a minimum 50-foot setback from domestic drinking water supply wells. Secondary recycled water requires a 100-foot setback.
• Cross-Connection Testing: Dual-plumbed buildings (using recycled water for toilet flushing or cooling towers) must undergo mandatory cross-connection shutdown tests prior to initial operation and at least once every 4 years thereafter.