California’s Title 22 drinking water standards are the state’s enforceable rules for what can be in the water delivered by public water systems, and they cover contaminant limits, testing schedules, public notification when something goes wrong, and treatment requirements for recycled water. The rules live in Division 4, Chapter 15 of the California Code of Regulations and apply to roughly 7,500 public water systems overseen by the State Water Resources Control Board. On many contaminants, California’s limits are stricter than the federal ones.
What Title 22 Covers
Title 22 as a whole is enormous, spanning 15 divisions on topics from child care licensing to hazardous waste.1Cornell Law Institute. California Code of Regulations Title 22 The drinking water piece is one specific slice: Division 4 (Environmental Health), Chapter 15, “Domestic Water Quality and Monitoring Regulations.”2Cornell Law Institute. California Code of Regulations Title 22 Division 4 Chapter 15 – Domestic Water Quality and Monitoring Regulations Separate chapters within Division 4 govern recycled water and also fall under the Title 22 umbrella.
The rules apply to all public water systems, both community systems that serve year-round residents and non-community systems that serve places like schools, office parks, and campgrounds. The State Water Resources Control Board oversees compliance through its Division of Drinking Water, which issues operating permits, inspects facilities, reviews water quality data, and takes enforcement action.3State Water Resources Control Board. Drinking Water Program
How California Compares to Federal Standards
The federal Safe Drinking Water Act lets the EPA set national standards, and states can take over enforcement (called “primacy”) if their rules are at least as strict.4EPA. Drinking Water Regulations California holds primacy and enforces both the federal Act and its own California Safe Drinking Water Act.5U.S. Environmental Protection Agency. Primacy Enforcement Responsibility for Public Water Systems
California often goes further than the federal floor. The state regulates hexavalent chromium and perchlorate at levels the EPA has not set enforceable federal limits for, and California’s MCL for fluoride is 2.0 mg/L, half the federal limit of 4.0 mg/L.6Cornell Law Institute. California Code of Regulations Title 22 Section 64431 – Maximum Contaminant Levels Inorganic Chemicals When the EPA adopts new regulations, California has up to two years to incorporate them.
Primary Maximum Contaminant Levels
The core protections are the primary Maximum Contaminant Levels, or MCLs. An MCL is the highest concentration of a contaminant legally allowed in water delivered to the public, and it is defined as the maximum permissible concentration established under the California Health and Safety Code or by the EPA.7Legal Information Institute. California Code of Regulations Title 22 Section 60301.575 – Maximum Contaminant Level or MCL Primary MCLs are legally enforceable because the substances they cover can cause illness.
Section 64431 lists MCLs for 19 inorganic chemicals. The ones most California consumers ask about:6Cornell Law Institute. California Code of Regulations Title 22 Section 64431 – Maximum Contaminant Levels Inorganic Chemicals
- Arsenic: 0.010 mg/L
- Fluoride: 2.0 mg/L
- Nitrate (as nitrogen): 10 mg/L
- Hexavalent chromium: 0.010 mg/L
- Perchlorate: 0.006 mg/L
- Mercury: 0.002 mg/L
Nitrate is a particularly common concern in California’s agricultural regions, where fertilizer runoff can push levels toward or past the MCL. Hexavalent chromium and perchlorate are California-specific standards the state added independently of federal requirements.
Section 64444 sets MCLs for dozens of organic chemicals, including pesticides, industrial solvents, and disinfection byproducts.8Legal Information Institute. California Code of Regulations Title 22 Section 64444 – Maximum Contaminant Levels Organic Chemicals Separate sections cover radioactive contaminants, with limits including 15 pCi/L for gross alpha particle activity, 5 pCi/L for combined radium-226 and radium-228, and 20 pCi/L for uranium.9State Water Resources Control Board. MCLs, DLRs, and PHGs for Regulated Drinking Water Contaminants
Secondary MCLs for Taste, Smell, and Appearance
Not every contaminant is a health threat. Secondary MCLs cover substances that affect what regulators call “consumer acceptance” qualities: taste, odor, clarity, and staining. Water above a secondary MCL will not make you sick, but it may look cloudy, taste metallic, or corrode fixtures. Key limits include:10State Water Resources Control Board. Secondary Drinking Water Standards
- Iron: 0.3 mg/L
- Manganese: 0.05 mg/L
- Total dissolved solids: recommended 500 mg/L, upper 1,000 mg/L, short-term 1,500 mg/L
- Chloride: recommended 250 mg/L, upper 500 mg/L
- Aluminum: 0.2 mg/L
- Odor threshold: 3 units
- Turbidity: 5 units
TDS, chloride, sulfate, and conductance use a three-tier range rather than a single hard cap. A system delivering TDS at 800 mg/L is within the upper range but will taste different from one running at 400 mg/L. No public health goals exist for secondary contaminants because these standards are based on aesthetics alone.
PFAS: An Evolving Area
Per- and polyfluoroalkyl substances, or PFAS, are synthetic chemicals found in firefighting foam, nonstick coatings, and food packaging. California does not yet have enforceable MCLs for PFAS, but the state has issued notification and response levels that require action when PFAS are detected. As of October 2025:11State Water Resources Control Board. PFAS Per- and Polyfluoroalkyl Substances Drinking Water Systems
- PFOA: notification level 4.0 ng/L, response level 10 ng/L
- PFOS: notification level 4.0 ng/L, response level 40 ng/L
A notification level triggers a requirement for the water system to inform the Division of Drinking Water and the local governing body. A response level goes further: the system should take the contaminated source out of service or treat it. California is developing formal MCLs for PFOA, PFOS, and several other PFAS compounds.
On the federal side, the EPA finalized enforceable MCLs of 4.0 parts per trillion for both PFOA and PFOS in April 2024.12Federal Register. PFAS National Primary Drinking Water Regulation Public water systems must complete initial monitoring by April 2027 and meet the MCLs by April 2029. California systems will need to comply with whichever standard is stricter once the state finalizes its own PFAS MCLs.
Monitoring and Testing
Contaminant limits mean nothing without testing. Title 22 sets monitoring schedules tied to the type of contaminant, the size of the system, and whether the source is groundwater or surface water. Bacteria testing is a good example: a community water system must collect a minimum number of routine bacteriological samples each month, scaled to population served or number of service connections, whichever produces more samples.13Legal Information Institute. California Code of Regulations Title 22 Section 64423 – Routine Sampling Smaller transient groundwater systems may test quarterly; seasonal systems test during operating months.
Chemical testing follows different cycles. Many synthetic organic chemicals are tested quarterly or annually depending on past detections and source vulnerability. Radioactivity testing runs on multi-year cycles. All samples must be collected according to the system’s sample siting plan and analyzed by state-certified laboratories.
What Happens When a System Violates a Standard
When a system exceeds an MCL or fails to treat water properly, it must notify the public, and how fast depends on how serious the problem is. California uses three tiers.
Tier 1 applies to situations with immediate potential health impact, like bacterial contamination or a treatment failure that could allow pathogens through. The system must consult with the state board within 24 hours, and if consultation does not happen in that window, issue public notice within 48 hours.14Legal Information Institute. California Code of Regulations Title 22 Section 64463.4 – Tier 2 Public Notice
Tier 2 covers MCL violations and treatment technique failures that do not pose an immediate risk. Customers must be notified as soon as possible, within 30 days of the system learning of the violation, though the system can request a 60-day extension. Tier 3 handles less urgent issues like monitoring lapses and reporting violations.
The state board can issue citations describing the violation and setting a correction deadline. Each citation can carry a penalty of up to $1,000 per day for each day the violation occurred and each day it continues, with separate penalties for each distinct violation, on top of any other liability under state or federal law. The board can also issue compliance orders requiring a system to repair or upgrade treatment, install new equipment, change its water source, or stop adding service connections until the problem is fixed. Additional monitoring can be ordered to verify a return to compliance.
How to Check Your Own Water
Every community water system in California must publish an annual Consumer Confidence Report disclosing what contaminants were detected, whether the system met all MCLs, and the potential health effects of any exceedances.15California State Water Resources Control Board. Consumer Confidence Reports Your system typically mails or emails the report each year, and copies are available online.
To look up compliance history and testing data directly, use the state’s Drinking Water Watch database at sdwis.waterboards.ca.gov. You can search by system name, county, or number to see violation history, enforcement actions, and water quality results. The state board also runs an electronic Annual Report system collecting data on system capacity, water quality, and financial health.16California State Water Resources Control Board. Electronic Annual Report If your water has a persistent taste, odor, or appearance issue, these resources can tell you whether your system is within its secondary MCLs or has known compliance problems.
Recycled Water Under Title 22
California’s chronic water scarcity makes recycled water an important resource, and Title 22 sets tiered treatment standards based on how likely the water is to reach people. Undisinfected secondary-treated recycled water can irrigate orchards and vineyards where the edible portion is not contacted by the water. Freeway landscaping and cemeteries require at least disinfected secondary-23 treated water. The most demanding non-potable uses (food crops where water touches the edible portion, parks and playgrounds, recreational lakes) require disinfected tertiary treatment.17Legal Information Institute. California Code of Regulations Title 22 Section 60304 – Use of Recycled Water for Irrigation18State Water Resources Control Board. State Board Division of Drinking Water Recycled Water Regulations
Indirect potable reuse projects, where treated wastewater eventually becomes part of the drinking water supply, must use “full advanced treatment”: reverse osmosis followed by an oxidation process. The reverse osmosis membranes must achieve at least 99% rejection of sodium chloride, and the oxidation process must remove specific indicator compounds by 0.5-log (69%) or more for most chemical groups.19Legal Information Institute. California Code of Regulations Title 22 Section 60320.201 – Advanced Treatment Criteria
Private Wells Are Not Covered
Title 22 applies only to public water systems. If your water comes from a private well, neither the EPA nor the state’s drinking water program regulates its quality, and responsibility for testing and safety falls on you as the homeowner.20US EPA. Private Drinking Water Wells Many California counties do not require ongoing sampling of private wells after installation. Periodic testing for bacteria, nitrate, and any contaminants common in your area is the only way to know whether your well water would meet the same standards public systems must.