How it's organized

• Study Guides — one page per rule or topic area containing purpose, rule evolution, key numbers (MCLs/MCLGs/MRDLs), monitoring & compliance mechanics, notification tiers, and California-specific requirements where they diverge from the federal rule. Listed alphabetically.
• Study Tools
  • Sample Exam Questions: scenario-based, framed around the REACT and CARES lenses
  • Flash Cards: quick recall, tracks right/wrong and lets you filter by category or missed cards

How to use it

• Click any Study Guide in the sidebar to jump straight to that rule's page.
• Use the Flash Cards deck to drill recall. Track accuracy and filter by "missed only" or by category for targeted review.
• Use Sample Exam Questions to rehearse verbal answers using the REACT (operations) and CARES (management) lenses.
• Click "CA SWRCB T5 Exam Dashboard" at the top of the sidebar anytime to return to this page.
• Switch between the Dark and Light buttons under the title anytime.

Source material

• T5 Examination Description
• Drinking Water-Related Regulations (Aug 2025)
• 40 CFR - Part 141
• EPA Quick Reference Guides
• National Primary Drinking Water Regulations
• The Microbial Toolbox
• CA Cryptosporidium Action Plan (April 2019)
• Filter Backwash Rule Technical Guidance Manual
• Lead and Copper Rule Improvements
• CA PFAS Information
• Upcoming CA Regulations

Regulated contaminants

*Routine TTHM/HAA5 monitoring frequency and number of locations are dictated by system type (Subpart H / surface water vs. ground water) and population served. Subpart H systems monitor more frequently and at more locations than ground water systems of the same size; the smallest systems monitor annually, larger systems quarterly.

Regulated disinfectants

Running Annual Average (RAA) & Locational Running Annual Average (LRAA)

Operational Evaluation Levels (OEL)

If an OEL is exceeded, the system must:

• Conduct an operational evaluation (examine treatment & distribution practices contributing to TTHM/HAA5 formation, and identify steps to minimize future exceedances).
• Submit a written report to the state no later than 90 days after being notified of the results that caused the exceedance.
• Keep a copy of the report and make it publicly available on request.

Enhanced coagulation — required TOC removal (%)

Subpart H systems using conventional filtration must remove specified percentages of TOC (treatment technique) unless they meet alternative criteria. Softening systems must meet removal for source alkalinity > 120 mg/L as CaCO₃.

Alkalinity in mg/L as CaCO₃.

Controlling TTHM & HAA5 — treatment techniques

DBPs form when chlorine reacts with natural organic matter (measured as TOC). Control works three ways — remove the organic precursors, manage the disinfectant, or cut contact time in the system. Most techniques lower both TTHM and HAA5; only pH control and aeration act on one type selectively.

Best Available Technologies per Title 22 Table 64533–B: enhanced coagulation, enhanced softening, GAC, and nanofiltration (paired with chlorine as primary + residual disinfectant), plus improved distribution & storage-tank management for consecutive systems. Dose/point optimization, tank turnover, flushing, pH control, and aeration are standard operating practice, not enumerated BAT. See the MCL table above for the TTHM/HAA5 limits.

Turbidity Requirements

*Exceeding the CFE max turbidity limit triggers DDW consultation within 24 hours. Failure to consult can escalate this to a Tier 1 Public Notification.

+Systems with ≤2 filters may monitor CFE continuously in lieu of IFE.

IFE FOLLOW-UP TRIGGERS

IFE triggers are based on two consecutive readings taken 15 minutes apart at the same filter.

FILTER BACKWASH RECYCLING REQUIREMENTS

Requirement figures above are design/operational guidelines/goals, not explicitly FBRR requirements - verify against your plant's permit.

Covered recycle flows

• Filter Backwash Waste — Particles dislodged from filter media when a filter is backwashed.
• Supernatant — Decant from a sedimentation basin used to hold solids.
• Dewatering Liquids — Liquids from a unit concentrating solids for disposal (DAF, Belt Press, etc.)

Recycle information to keep on file

• List of all recycle flows and the frequency they are returned.
• Average and maximum backwash flow rates and backwash duration
• Typical filter run length and a written summary of how it is determined.
• Type of treatment provided for waste flows and for recycle flows.

LT2 — Cryptosporidium bin classification

Bin concentration = average of individual sample results over the monitoring round. Large systems (≥10,000) sample Cryptosporidium, E. coli & turbidity monthly for 2 years; small systems (<10,000) sample E. coli every 2 weeks for 1 year (Cryptosporidium only if E. coli triggers). Second round begins 6 years after initial bin classification.

Microbial Toolbox

The Microbial Toolbox is a EPA Technical Guidance Manual that outlines the set of "tools" a Water System can use to meet the additional Cryptosporidium treatment required by its LT2 bin classification. Systems may combine any of the applicable options below provided design, operational, and performance criteria are met.

• Source: watershed control program; alternative source/intake management
• Pre-Filtration: pre-sedimentation w/coagulation; two-stage lime softening; bank filtration
• Treatment Performance: combined filter; individual filter; demonstration of performance
• Additional Filtration: bag/cartridge; membrane; second-stage; slow sand
• Inactivation: chlorine dioxide; ozone; UV.

Cryptosporidium Action Plan

The CAP is a DDW technical guidance document that clarifies how a surface water system in California optimizes its treatment process to meet existing regulatory requirements. It does not impose additional requirements beyond those outlined above.

The CAP's authority is derived from the California Health and Safety Code (§116360) and includes:

• Watershed Sanitary Surveys — a comprehensive survey of a watershed's contamination sources.
• Source Bacteriological Monitoring — monthly raw water monitoring for E. coli.
• Treatment Optimization Goals:
  • Settled Effluent: 1-2 NTU
  • Filter Backwash: 10% and <2.0 NTU
  • CFE <0.1 NTU
• Operations Plan — incorporate the goals above into the Operations Plan.
• Reliable Processes — alarms, standby/redundant equipment and processes.
• Alternate Treatment Technology — LT2 bin classification treatment options (see Microbial Toolbox).
• Public Communication — Cryptosporidium language for the Consumer Confidence Report (CCR) and Fact Sheet.

Figures above are design/operational guidelines/goals, not explicitly SWTR requirements - verify against your plant's permit.

Disinfection & residual monitoring

Residual disinfectant must be maintained and monitored at the points below.

Systems must also meet Stage 1 & 2 DBPR MRDLs and MCLs.

Disinfection profiling & benchmarking

The purpose of disinfection profiling and benchmarking is to allow systems and States to assess whether a change in disinfection practices reduces microbial protection. Systems must develop a disinfection profile that reflects Giardia and viruses inactivation, calculate a benchmark based on the profile, and consult with the State prior to making a significant change* to disinfection practices.

• Disinfection Profile — a graphical representation of a system's microbial inactivation over 12 consecutive months.
• Disinfection Benchmark — the lowest monthly average inactivation value.

*A Significant Change is defined as: change in point of disinfection, change in type of disinfectant, change in disinfection process, or any other modification designated by the state.

Compliance Monitoring

A system can avoid triggered monitoring by notifying the state in writing that it provides ≥4-log virus treatment (inactivation, removal, or a state-approved combination) before or at the first customer, then monitoring to demonstrate it.

Chemical Disinfection

Membrane filtration: State-specified — monitor process & verify membrane integrity.
Alternative / UV: State-specified — UV: monitor intensity, flow, lamp status; verify sensor calibration ≥ monthly; validate reactor.

Continuous-Monitoring Equipment Failure

• On failure, conduct grab sampling every 4 hours until the equipment is back in service.
• Resume continuous monitoring within 14 days.

Notifications

• Failure to maintain 4-log virus inactivation treatment → Tier 2 Public Notification
  • Occurs when 4-log virus inactivation treatment is not restored within 4 hours — notify DDW ASAP.
• Failure to conduct required compliance monitoring → Tier 3 Public Notification.

Triggered Monitoring

Systems not providing 4-log virus inactivation treatment must perform triggered source-water monitoring from any source in use when the PWS (or a purchasing system, if a wholesaler) receives a total coliform-positive routine sample result (TCR/RTCR).

• Samples must be collected within 24 hours.
• Samples must be taken before treatment (or at a state-approved location following treatment).
• Samples must be analyzed for fecal coliforms (E. coli, enterococci, or coliphage).

A PWS that voluntarily discontinues 4-log treatment before/at the first customer makes the system subject to triggered source-water monitoring.

Notifications

• Fecal-indicator-positive source sample → Tier 1 Public Notification
• Failure to conduct required triggered / additional monitoring → Tier 3 Public Notification

Exceptions & invalidation

• Distribution-system cause: not required to conduct triggered monitoring if the state documents the TC+ was caused by a distribution deficiency, or the system shows (within 30 days) the sample met state criteria for distribution conditions causing TC+.
• Invalidation: state may invalidate a fecal-positive source sample on written lab notice of improper analysis, or substantial evidence the sample does not reflect source-water quality. If invalidated, resample for the same indicator within 24 h.

Sanitary Surveys

A DDW-conducted assessment of a GWS's performance. GWSs are surveyed every 3 years. This can be increased to every 5 years if:

• the PWS provides 4-log treatment of viruses, or
• has an outstanding performance record (as defined by the state) and no history of total coliform MCL or monitoring violations (TCR) since the last Sanitary Survey was conducted.

Treatment Technique

A GWS must implement one or more corrective actions if a significant deficiency is identified:

• Correct all significant deficiencies
• Provide an alternate source of water
• Eliminate source of contamination
• Provide 4-log treatment of viruses

Bacteriological sample siting plan (BSSP)

Every PWS must maintain a written BSSP identifying distribution system sampling locations that represent system water quality and the collection schedule for all Routine & Repeat sampling sites.

Routine samples

• Collected at regular intervals throughout the month.
• Minimum sample count is dictated by system type (ground water vs. surface water) and population served or number of service connections (whichever results in the larger amount of required samples).
• Each TC+ routine sample must be tested for E. coli and a Repeat Sample Set collected.
• Any EC+ result must be reported to the State by the end of that day.

Repeat sample set

Within 24 hours of a TC+ result, the PWS must collect a Repeat Sample Set consisting of:

• Repeat Sample: One sample from the same tap as the original sample
• Upstream Sample: One sample collected within 5 service connections upstream of the original sample
• Downstream Sample: One sample collected within 5 service connections downstream of the original sample

If any sample from the Repeat Sample Set is TC+, it must be analyzed for E. coli (any EC+ sample must be reported to the State by end of day) and another Repeat Sample Set collected unless an assessment is triggered by the State.

E. coli MCL violation combinations

An EC+ result must be reported to the state by the end of the day the PWS is notified.

Assessments & corrective action

Purpose: find sanitary defects that could provide a pathway for microbial contamination or indicate failure of protective barriers.

Deadline: submit the assessment form within 30 days of the trigger; corrective actions completed no later than form submission, or within a state-approved timeframe proposed on the form.

Treatment-technique violations

• Failure to conduct a Level 1 or Level 2 assessment within 30 days of a trigger.
• Failure to correct all sanitary defects from an assessment within 30 days (or the state-approved timeframe).

What arsenic is and why it's a health concern

• Arsenic is a naturally occurring semi-metal found in rock and soil. It gets into water mainly by erosion of natural deposits, which is why it shows up in groundwater. Historic sources also include runoff from orchards (old arsenical pesticides) and wastes from glass and electronics manufacturing.
• In California groundwater it is one of the two most common regulated primary inorganic chemicals, along with nitrate.
• Arsenic is a known human carcinogen. Long-term exposure is linked to cancer of the bladder, lung, and skin, plus non-cancer effects: skin damage and circulatory (blood vessel) problems.
• Because it is a carcinogen, the health goal (maximum contaminant level goal, MCLG) is set at zero. No level is considered risk-free; the enforceable limit balances health protection against the cost and feasibility of removal.
• It is a chronic contaminant, not acute. An exceedance calls for a deliberate response, not immediate plant shutdown, except at very high levels (see the Title 22 mechanics section below).
• Revised, not repealed: the MCL was tightened from 50 ppb to today's 10 ppb, effective January 23, 2006.

Best Available Technologies (BAT)

California (Title 22 §64447.2) and federal rules (40 CFR §141.62(c)) name the same seven best available technologies for arsenic. Only the numbering differs between the two lists.

• Activated alumina
• Coagulation/filtration (not a BAT for systems under 500 service connections)
• Ion exchange
• Lime softening (not a BAT for systems under 500 service connections)
• Reverse osmosis
• Electrodialysis
• Oxidation/filtration (for high removal, the iron-to-arsenic ratio must be at least 20 to 1)

All seven remove arsenate, As(V) or As+5. Arsenite, As(III) or As+3, is uncharged and removes poorly, so systems pre-oxidize to convert As(III) to As(V) before treatment.

Compliance determination (IOCs, VOCs, SOCs)

• Compliance based on a running annual average at each sampling point.
• No violation until 1 year of quarterly samples collected — unless fewer samples would already cause the RAA to be exceeded.
• If not all required samples are collected, compliance is based on the RAA of the samples collected.

Monitoring for total arsenic

Samples collected at each water source, or at each entry point to distribution representative of each source after treatment (Title 22 §64432(e)). Waivers: after ≥3 rounds of monitoring (3 compliance periods for ground water; 3 years for surface water) with all results below the MCL, a system may apply for a waiver of up to one 9-year compliance cycle — but must still collect ≥1 sample per source while the waiver is in effect (§64432(m)).

Title 22 mechanics (CA-specific)

• MCL exceedance (§64432(g)): confirm the result and notify the State Board. Increased (quarterly) monitoring then applies per the table above.
• More than 10× the MCL (§64432(h)): the State Board may direct immediate source removal, with written State approval required before the source returns to service.
• Consumer Confidence Report statement: required when arsenic is above half the MCL (0.005 mg/L) but at or below it. See the Consumer Confidence Report page.

What radionuclides are and why they're a health concern

• Radionuclides are radioactive forms of elements. Gross alpha emitters, radium-226, radium-228, and uranium occur naturally and get into water by erosion of natural deposits, so they show up mainly in groundwater.
• Beta particle and photon emitters are mostly man-made. They are a concern only at systems the State designates as vulnerable, such as those downstream of a nuclear facility.
• Long-term exposure raises the risk of cancer. Uranium also causes toxic effects on the kidneys.
• Because they are carcinogens, the health goal (maximum contaminant level goal, MCLG) is zero for all of them. No level is considered risk-free.
• These are chronic contaminants, not acute. An exceedance calls for a deliberate response, not immediate plant shutdown.

MCLs (MCLG = 0 for all)

*Up to 168 individual beta/photon emitters may be used to calculate compliance.

Uranium: California's MCL of 20 pCi/L is by radioactivity and is stricter than the federal MCL of 30 µg/L (by mass) shown on the Drinking Water Standards page (that table shows federal values). It is the operative limit for a California system. Gross alpha (15 pCi/L) and combined radium (5 pCi/L) match federal.

Beta/photon equivalents: California expresses the 4 mrem/yr dose limit as specific activities: strontium-90 = 8 pCi/L, tritium = 20,000 pCi/L.

Detection levels for reporting (DLRs) set the "detection limit" used in the reduced-monitoring tiers below: radium-226 and radium-228 each 1 pCi/L, gross alpha 3 pCi/L, uranium 1 pCi/L, gross beta 4 pCi/L.

Best Available Technologies (BAT)

California (Title 22 §64447.3) and federal rules (40 CFR §141.66) name the same best available technologies, which vary by radionuclide:

• Combined radium-226/228: ion exchange, reverse osmosis, lime softening
• Uranium: ion exchange, reverse osmosis, lime softening, coagulation/filtration
• Gross alpha particle activity: reverse osmosis
• Beta particle and photon radioactivity: ion exchange, reverse osmosis

Ion exchange and reverse osmosis are the workhorses across the board. The catch is residuals: spent resin, regenerant brine, and reverse-osmosis reject water concentrate the radioactivity and need proper disposal.

Monitoring — gross alpha, radium, uranium

Beta particle & photon radioactivity

• No monitoring required for most CWSs. Vulnerable CWSs: gross beta quarterly; tritium & strontium-90 annually.
• Reduced: if RAA of gross beta minus naturally occurring K-40 ≤ 50 pCi/L → 1 sample every 3 years.
• Increased: if it exceeds 50 pCi/L → speciate as required and sample at initial frequency.

All samples at each entry point to distribution.

How the rule evolved: LCR → LCRR → LCRI

The Lead and Copper Rule (LCR, 1991) and its two rebuilds: the Lead and Copper Rule Revisions (LCRR, 2021) and the Lead and Copper Rule Improvements (LCRI, 2024). This table shows what each version changed and what it left alone.

*Based on 90th percentile sample results

Treatment technique responses if AL exceeded

An AL exceedance is not itself a violation. The exceedance triggers the below responses under today's rules. The responses cascade in order of cost and disruption by targeting water chemistry treatment first, and replacing lead service lines only if that is not enough.

Under the LCRI this changes, and service line replacement becomes a standing requirement rather than a last step.

• Public Outreach & Education (lead only):
  • A lead action level exceedance requires a Tier 1 public notice to all consumers within 24 hours.
  • Deliver educational materials within 60 days after the end of the monitoring period. While the exceedance continues, repeat annually and include a message on each water bill at least quarterly. Not required for a copper-only exceedance.
• Water Quality Parameter (WQP) Monitoring:
  • No existing Corrosion Control Treatment (CCT): baseline water chemistry (pH, alkalinity, calcium, conductivity, temperature) that helps the State decide what corrosion control to require.
  • Existing CCT: the same parameters plus the inhibitor residual already dosed (orthophosphate for a phosphate inhibitor, silica for a silicate inhibitor).
  Once CCT is running, monitor at the tap every 6 months and at each entry point every 2 weeks to confirm you are holding the State-set OWQPs.
• Corrosion Control Treatment (CCT) - The State designates one or more of three treatments:
  • Alkalinity and pH Adjustment - Raise pH (caustic soda, lime, etc.) and hold alkalinity so lead and copper stay less soluble and a stable protective scale forms. Usually the first and lowest-cost option, but increasing pH affects disinfection efficacy and byproduct formation.
  • Corrosion Inhibitor - Feed orthophosphate (or a silicate) to build a protective film on the pipe and hold a residual to the tap. The workhorse for lead, but phosphate adds load to downstream wastewater and needs a constant, reliable feed.
  • Calcium Hardness Adjustment. Adjust calcium and carbonate to lay a thin calcium carbonate film on the pipe. Seldom the primary fix for lead; mainly for soft, low-calcium water.
  Once the State designates the required CCT, install it within 24 months, then run 2 consecutive 6-month rounds of tap and WQP monitoring. The State then sets optimal WQPs (OWQPs) that define your corrosion control treatment requirements.
• Source Water Treatment (SOWT) - Within 6 months of the exceedance, sample each source entry point to measure how much lead or copper comes from the source, then recommend treatment or show it is not needed. If required, install within 24 months. The State sets maximum permissible source levels.
• Lead Service Line Replacement (LSLR) - Used only if the lead AL is still exceeded after CCT and SOWT. Replace at least 7% of lead service lines per year. Under the rules in force now, a line also counts as "replaced" if its own samples are at or below the lead AL ("replaced through testing").
• Stopping - Discontinue public outreach and LSLR once the 90th percentile stays at or below the lead AL for 2 consecutive 6-month periods. Resume if it is exceeded again.

Meeting the LCRI

The LCRI is a multi-year program. What changes is in the table above. Here is how a system gets ready, with public health first throughout.

• Service Line Inventory - The inventory becomes the replacement roadmap. Keep it current and resolve every unknown-material line.
• Replacement Program - Replacement becomes mandatory for every lead line and every galvanized line that requires replacement, on the roughly 10-year clock in the table, regardless of tap sampling results. Budget and plan for it now (funding through state revolving fund loans, grants, and rates, contractors lined up, and a maintainable yearly pace to stay on schedule).
• Corrosion Control (Lower AL) - The lead action level drops. Re-check existing corrosion control treatment against the tighter number and plan for re-optimization the LCRI requires after an action level exceedance.
• Tap Sampling - Sampling moves to the new first-and-fifth-liter method at lead service line sites (see the table). Identify qualifying sites, train samplers, and update procedures ahead of the date.
• Schools & Child Care Facilities - Develop or improve the expanded sampling and outreach program for schools and licensed child-care facilities.
• Public Outreach - Start customer communication early, coordinate funding with your governing board, and plan staffing for the added workload. Be prepared to issue timely (Tier 1) public notification if the lead action level is exceeded. Update revised lead language within the CCR.
• California timing - The State's adoption of the LCRI into Title 22 and the current California action level are tracked on the Rulemaking Pipeline page.

Background

• Manganese is the 12th most abundant element in the earth's crust; naturally occurring in both surface water and groundwater.
• It is an essential nutrient, but over-exposure poses a neurotoxic risk; occupational exposure causes manganism, a cognitive/motor syndrome resembling Parkinson disease.
• Main absorption route is the gastrointestinal tract (inhalation secondary; dermal not significant).
• Formula-fed infants are the most susceptible population — they absorb and/or retain more manganese than adults. This is the driver of the 2026 revision.
• Aesthetic effects at lower concentrations: discolored water, staining of plumbing fixtures and laundry, sediment buildup.

Current regulation — the secondary MCL

• Secondary MCL: 0.05 mg/L, established for aesthetics (discoloration), not health.
• In California, secondary MCLs are enforceable (U.S. EPA's identical 0.05 mg/L secondary standard is a non-enforceable guideline). Exam-critical distinction.
• CA secondary MCLs apply only to community water systems — nontransient noncommunity systems (schools, workplaces) do not get the benefit of the secondary standard.

See the Secondary MCL table on the Drinking Water Standards page.

June 2026 revised NL and RL

• NL exceedance → notify the governing body within 30 days (Health & Safety Code §116455).
• RL exceedance (a single confirmed detection — take a repeat sample and average the two) → notify DDW within 7 days, and a community water system must, within 30 days of the initial exceedance, either notify customers to use an alternative water source (e.g., bottled water) when preparing infant formula or mitigate (take the source offline / treat).
• The RL is set at 4× the NL — an unusually tight multiple; most non-cancer response levels are 10× the notification level.

DDW derived a health-protective concentration (HPC) of 0.02 mg/L as the health basis, but set the NL higher at 0.05 mg/L to line up with the enforceable secondary MCL (0.05 mg/L) and the 0.05 mg/L bottled-water limit — which gives the Board authority to require community-system public notice.

Comparison advisories for context: U.S. EPA health advisory 0.3 mg/L (2004); WHO provisional health-based guideline 0.8 mg/L (2021).

Exam trap: the secondary MCL and the new NL are numerically identical (0.05 mg/L) but distinct — different purpose (aesthetic standard vs. health-based advisory), different compliance basis, different applicability. An exam question can probe exactly this.

The path to a primary MCL

• June 2, 2026: DDW requested OEHHA establish a PHG for manganese.
• The CA ladder: occurrence/health data → NL/RL (HSC §116455/§116456) → PHG (OEHHA, HSC §116365(c)) → primary MCL set as close to the PHG as technologically and economically feasible (HSC §116365(a)).

See the PFAS page for the parallel example of the same ladder in motion.

What are PFAS?

PFAS are a group of more than 14,000 human-made substances that are characterized by a strong carbon-fluorine bond. In typical conditions, PFAS are resistant to degradation and do not break down in the environment (commonly called "forever chemicals"). PFAS are widely used as surface coatings in consumer, commercial, and industrial products such as carpet, clothing, food packaging, non-stick cookware, firefighting foam, etc.

Health concern

PFAS exposure may result in adverse health effects including developmental effects to fetuses during pregnancy, cancer, liver effects, immune effects, thyroid effects, and other effects.

Sources and occurrence

Detected in air, water, wastewater, fish, and soil worldwide, PFAS are especially present in and around facilities that produce, use or dispose of PFAS or PFAS containing materials.

Four major sources of PFAS in drinking water

• Fire training and response sites
• Industrial sites
• Landfills
• Wastewater treatment plants and biosolids

Federal — 2024 PFAS NPDWR

On April 10, 2024, the U.S. EPA announced the final National Primary Drinking Water Regulation (NPDWR) for six PFAS establishing legally enforceable MCLs, plus a Hazard Index (HI) MCL for PFAS mixtures.

Hazard Index concept (exam-testable): a sum of fractions, where each fraction compares the measured level of a PFAS to the highest level below which there is no risk of health effects; the HI MCL is set at 1.

Federal MCLs and California NL/RL

Values are ng/L (= parts per trillion, ppt) unless noted. PFHxA is in µg/L (1.0 µg/L = 1,000 ng/L). PFBS has an MCLG but no individual MCL; the Hazard Index is unitless.

Federal MCLs and MCLGs finalized April 2024. California NL and RL issued or revised October 29, 2025, except PFBS (March 5, 2021); PFHpA requested.

Monitoring & Notification Requirements

Federal Compliance Timeline

Notification Level (NL): a nonregulatory, health-based advisory level for a contaminant without an MCL. Response Level (RL): set higher than the NL — the recommended concentration at which systems consider taking a source out of service or providing treatment. As a rule of thumb the RL is 10× the NL for non-cancer endpoints and 100× the NL for cancer endpoints set at the 10⁻⁶ risk level, though individual chemicals vary (manganese, for example, is 4×).

Applies to systems that receive a DDW monitoring order; the RL response requirement has been in force since January 2020.

See the combined Federal MCLs and California NL/RL table above for NL and RL values.

Compliance checklist

• Know your source vulnerability: proximity to the four major source categories (fire training sites, industrial sites, landfills, WWTP/biosolids); groundwater sources are the accumulation risk.
• Complete initial monitoring by 2027.
• Track results against NLs and RLs; execute the required response(s) on NL or RL exceedance.
• Report confirmed detections in the CCR.
• Plan for federal MCL compliance by 2029 and watch California's own MCL rulemaking.
• Pursue funding where needed — State Water Board PFAS grants/loans and EPA's Emerging Contaminants in Small or Disadvantaged Communities grant.
• Evaluate treatment feasibility early for affected sources:
  • Granular Activated Carbon (GAC)
  • Ion Exchange
  • Reverse Osmosis (RO) or High-Pressure Membranes
• Maintain records of monitoring results, lab reports, order correspondence, and public notifications, consistent with the Record Keeping Rules page of this dashboard.

How California makes an MCL

California builds a primary MCL through a defined statutory ladder, not by direct EPA adoption:

Contaminant identified (occurrence data / UCMR / monitoring orders) → NL/RL issued (HSC §116455) → OEHHA sets a PHG (HSC §116365(c)) → DDW sets the primary MCL as close to the PHG as technologically and economically feasible (HSC §116365(a)) → adoption into Title 22.

DDW must also review existing MCLs against current PHGs at least every five years (the quinquennial MCL review) — this review is what generates most of the revision items below.

Hexavalent chromium — adopted, but compliance is phasing in now

• Cr(VI) MCL: 0.010 mg/L (Table 64431-A); DLR 0.0001 mg/L (Table 64432-A). Analysis by EPA Method 218.6 or 218.7. Rule effective October 1, 2024; the MCL itself applies on the phased compliance dates below.
• CA total chromium MCL: 0.05 mg/L — stricter than the federal total chromium MCL of 0.1 mg/L shown on the Drinking Water Standards page (that table shows federal values).

• Initial monitoring: community and NTNC systems had to begin Cr(VI) compliance monitoring by April 1, 2025 — six months after the Oct. 1, 2024 effective date (§64432(b)).
• §64432(q): an MCL exceedance before your compliance date → submit a Hexavalent Chromium MCL Compliance Plan within 90 days (compliance method; pilot study if new/modified treatment; construction dates; Operations Plan date).
• §64432(r): new/modified treatment requires a State Board-approved Hexavalent Chromium Operations Plan before serving treated water (performance monitoring, maintenance program, unit process descriptions, dose-rate procedures, reliability features).

MCLs in development

• PFAS — CA MCL rulemaking (SWRCB-DDW-24-001) underway; federal 2024 NPDWR MCLs in force with 2026 federal proposals pending. Full treatment on the PFAS page.
• NDMA (N-nitroso-dimethylamine) — MCL in development (SWRCB-DDW-22-006). Operator relevance: a nitrosamine DBP associated with chloramination.
• Disinfection byproducts — TTHM and HAA5 MCL revisions under consideration. Current Stage 1/2 framework on the Stage 1 & 2 DBP Rules page.
• Styrene — MCL revision in process (current CA/federal MCL 0.1 mg/L per the Drinking Water Standards page).
• Cadmium and mercury — MCL revisions in process (quinquennial-review outcome).
• 1,4-Dioxane — MCL development.
• Arsenic — CA MCL revision in process (current 0.010 mg/L framework on the Arsenic Rule page; the 2004 PHG of 0.004 µg/L implies downward pressure — an inference, not a proposed number).

NL/RL watch list

• Manganese — revised June 2, 2026; full treatment on the Manganese page.
• Cyanotoxins — NLs under development (HABs program). Ties to the algae-bloom operations scenario in the Study Tools.
• PFHpA — NL/RL requested; see the PFAS page NL/RL table.

Lead and Copper Rule Improvements — CA implementation

The federal LCRI timeline and requirements live on the Lead and Copper Rule page ("How this rule evolved," the evolution table, and the "Meeting LCRI" compliance plan). This entry adds only the California layer:

• DDW is pursuing primacy for the federal LCR revisions (Upcoming Regulations "Primacy Package Approvals" list) and developing California enhancements.
• DDW proposes to adopt the federal LCRI as a new Title 22 Chapter 17.6 ("Control of Lead and Copper"), effective Nov 1, 2027, with the existing Chapter 17.5 repealed the same day — moving as an emergency rulemaking (State Water Board LCRI Regulations page, as of July 2026). Until then, the codified CA numbers stay on the old framework (lead AL 0.015 mg/L, §64678(d)).
• DDW held a public workshop on LCRI implementation June 11, 2026 (comments were due June 22, 2026), covering both the Ch. 17.6 adoption and the Assembly Bill (AB) 1096 school/child-care policy handbook.

Other pending items

• Cross-Connection Control Policy Handbook (CCCPH) — replaced Title 17's cross-connection provisions; revisions adopted and in effect April 21, 2026; phased implementation deadlines continue (plans, hazard assessments, specialist/tester certifications).
• Detection Limits for Purposes of Reporting (DLRs) — updates in process for metals and organic chemicals.
• Electronic Reporting of Drinking Water Quality Data — emergency regulation approved and in effect July 13, 2026.
• Primacy package approvals in progress — Public Notification Rule, Ground Water Rule, Revised Total Coliform Rule, PFAS NPDWR, LCR and revisions, CCR Rule.
• CCR Rule Revisions — already covered in the status callout on the CCR page (2027 changes).
• Recently landed (context, not pending): Direct Potable Reuse regulations; Onsite Treatment and Reuse of Nonpotable Water regulations — approved and in effect April 22, 2026.
• Microplastics — monitoring via policy handbook (SB 1422), not a numeric standard; awareness item only.

CCCPH deadline specifics beyond the April 21, 2026 effective date were not verified in this research and are intentionally omitted.

Scope

Counts & exceptions: 15 IOCs (nitrate, nitrite, asbestos are SMF exceptions) · 51 SOCs & VOCs (vinyl chloride for ground water is an exception) · 4 radionuclides (excludes beta/photon emitters).

Sampling-frequency legend

Frequency logic by contaminant group

"R&C < MCL" = primacy agency has determined the point is reliably and consistently below the MCL.

Key conditions (footnotes)

• Trigger levels: quarterly sampling is triggered at > MCL (IOCs), > detection limit (VOCs/SOCs), or ≥ ½ MCL (nitrate/nitrite). No R&C < MCL determination for surface-water nitrate.
• If the RAA of quarterly sampling is > MCL, remain quarterly until qualifying as R&C < MCL.
• Annual samples taken in the quarter that previously gave the highest result.
• SOC/VOC waiver: apply after 3 consecutive annual results below detection; vulnerability reconfirmed every 3 years (VOC waiver effective 2 periods / 6 years).
• Asbestos: monitor in the 1st 3-year period of each 9-year cycle (tap served by A-C pipe, or each EPTDS if source-vulnerable).
• Nitrate MCL of 20 mg/L may be approved for NCWSs not serving children under 6 months if criteria met (§141.11(d)).

Annual deadlines

• A wholesale CWS must deliver the information needed to prepare a CCR to its purchasing system(s) by April 1st, or a date mutually agreed upon and specifically included in the contract.
• CWSs must distribute their CCR to its customers and DDW by July 1st.
• CWSs must submit proof of CCR distribution to DDW by October 1 (or 90 days after distribution).

Eight required content items

Reporting & recordkeeping

• Mail or directly deliver a copy to each customer; make a good-faith effort to reach non-bill-paying consumers.
• Large-population non-English communities: include information in the appropriate language(s) or a contact for a translated copy.
• CWS serving ≥ 100,000 must also post the current report on a publicly accessible website.
• All CWSs must make copies available on request.

Now vs Revised CCR Rule

CA column: Title 22 as compiled Aug 2025 (project file) plus DDW's 2025 CCR-cycle instructions. EPA column: 2024 CCR Rule Revisions (89 FR 45980, May 24, 2024). CA adoption timing unconfirmed — verify before exam.

Tier 1  Within 24 hours

• Fecal coliform / E. coli present in a distribution sample; failure to test after a TC-positive.
• Nitrate, nitrite, or total nitrate+nitrite MCL violation; failure to take a confirmation sample.
• Chlorine dioxide MRDL violation in the distribution system (per the rule's conditions).
• Exceedance of the maximum turbidity level, if elevated to Tier 1 by the primacy agency.
• A treatment-technique violation posing an acute risk to health (e.g., failure to filter or disinfect under the SWTR/IESWTR/LT1/LT2), as determined by the primacy agency.
• Lead action level exceedance under the Lead and Copper Rule (LCRR/LCRI).
• Waterborne disease outbreak or other emergency.
• Detection of E. coli, enterococci, or coliphage in a ground water source sample.
• Other violations/situations determined by the primacy agency.

Tier 2  As soon as practical, within 30 days

• All MCL, MRDL, and treatment-technique violations except where Tier 1 is required.
• Monitoring violations, if elevated to Tier 2 by the primacy agency.
• Failure to comply with variance/exemption conditions.
• GWR 4-log systems: failure to maintain treatment for more than 4 hours.
• Failure to take required corrective action for a fecal-positive source or a significant deficiency (GWR).

Repeat every 3 months until resolved.

Tier 3  Within 12 months

• Monitoring / testing-procedure violations (unless elevated), including failure to profile/benchmark or to develop a monitoring plan.
• Operating under a variance or exemption.
• Special notices: unregulated-contaminant results; fluoride SMCL exceedance.

Repeat annually while unresolved.

Ten required elements of a notice

General retention requirements

May keep actual lab results or summaries (see 40 CFR 141.33). Requirements may not apply to systems that purchase water and add no treatment — check with the state.

Rule-specific retention

Phase II/V and the SWTR add no rule-specific retention beyond the general table. IESWTR applies to systems > 10,000 and is not covered by this small-system guide.

Why keep records

• Support proper operation & maintenance and efficient facility performance.
• Educate new staff; help recognize, diagnose, and solve problems.
• Resolve customer complaints; document changes in water use, quality, and availability.
• Facilitate communication with customers, regulators, and decision-makers; support financial planning and required reports.

Regulated contaminants (A–Z)

Units are mg/L unless noted (mg/L ≈ ppm). Health effects are from long-term exposure unless marked short-term. See detailed rule panels (DBPR, Arsenic, Radionuclides, Lead & Copper, TCR/RTCR, SWTR, PFAS) for monitoring & compliance mechanics — this table is the contaminant-by-contaminant limit/goal reference. PFAS are shown separately below (not part of the original 2009 poster).

Selected PFAS (2024 NPDWR)

New since the 2009 poster — finalized in EPA's April 2024 PFAS NPDWR. Full Hazard Index mechanics, California NL/RL levels, and the monitoring/compliance timeline are on the PFAS page; the current values are repeated here for a single contaminant-by-contaminant reference.

Units are ng/L (parts per trillion, ppt) except the Hazard Index, which is unitless — matches the PFAS page.

National Secondary Drinking Water Regulations

Non-enforceable federal guidelines for contaminants causing cosmetic (skin/tooth discoloration) or aesthetic (taste, odor, color) effects. EPA recommends but does not require compliance — some states, including California, adopt secondary MCLs as enforceable standards (Title 22 §64449).

California caveats (Title 22 governs a CA system)

This page is the federal NPDWR summary. For a California system, Title 22 governs and is more stringent in several places relevant to the exam:

• Hexavalent chromium (Cr6): no separate federal MCL (federal chromium above is total chromium at 0.1 mg/L) — California has its own Cr6 MCL of 0.010 mg/L. See the Rulemaking Pipeline page.
• Manganese: federally only a secondary standard (0.05 mg/L, above) — not a federal primary MCL. See the Manganese page for California's status.
• Lead action level: both federal and California currently enforce 0.015 mg/L; the federal LCRI value of 0.010 mg/L begins November 1, 2027. See the Lead and Copper Rule page.
• PFAS: California has its own Notification/Response Levels and MCL rulemaking that may differ from the federal MCLs above — do not assume the federal numbers are the CA compliance numbers. See the PFAS page.
• Uranium: federal MCL is 30 µg/L (above); California's operative MCL is 20 pCi/L (by radioactivity, not mass) — see the Radionuclides Rule page.

For the enforceable legal text, cite 40 CFR Part 141 (federal) or Title 22 (California) — not this summary.