CCR Glossary

Consumer Confidence Reports are full of regulatory shorthand — MCLs, TTs, RAAs, NTUs — and readers who don't live in the compliance world every day deserve clear definitions. This glossary covers every significant term you'll encounter in a CCR or in a conversation about federal drinking water rules, organized A to Z.

Terms with their own detail pages are linked out. Everything else is defined here with the precision the regulation actually uses.

Jump to: A · B · C · D · E · F · G · H · L · M · N · P · R · S · T · U · V · W

A

Action Level (AL) — The concentration of lead or copper in drinking water that, when exceeded at the 90th percentile of tap samples, triggers mandatory follow-up actions by the water system. Not a legal limit in the same sense as an MCL; crossing it starts a clock on corrosion control and service line replacement, not an immediate violation. See the full entry for how AL interacts with the LCRI's 2027 changes.

90th Percentile — The lead or copper concentration value at or below which 90 percent of the tap samples collected during a monitoring period fall. Under the Lead and Copper Rule and its successors, a system exceeds the action level when the 90th percentile sample result is above the threshold — currently 15 µg/L for lead (lowering to 10 µg/L beginning November 1, 2027). The 90th percentile is not an average; it is a ranked-sample threshold calculated from the system's full sampling set. See 40 CFR § 141.80.

AWIA (America's Water Infrastructure Act of 2018) — Federal legislation (Pub. L. 115-270) that amended the Safe Drinking Water Act and, among other things, required EPA to revise the CCR rule to add biannual delivery for large systems. The statutory chain is SDWA 1996 → AWIA 2018 → the May 2024 CCR Rule revisions. See 42 U.S.C. § 300g-3(c)(4).

B

Best Available Technology (BAT) — The treatment method EPA has determined to be the most effective means of reducing a contaminant to or below its MCL, taking cost into account. When EPA sets an MCL, it must also identify the BAT for that contaminant. BAT is relevant to CCRs when a system uses a treatment technique in lieu of a measurable MCL, since the TT is typically the BAT for that contaminant. See 40 CFR § 141.61.

C

Coliform (Total Coliform / E. coli) — Bacteria used as indicators of potential fecal contamination in drinking water. Total coliform presence in a distribution system sample triggers additional sampling and, depending on results, a public notification requirement. A positive E. coli result is a more serious acute MCL violation. CCRs must report any coliform-related violations that occurred during the reporting year. See 40 CFR Part 141 Subpart Y (Revised Total Coliform Rule).

Compliance Period / Compliance Cycle — A defined time interval during which a water system must collect a required number of samples to demonstrate it meets an MCL or treatment technique requirement. For disinfection byproducts, compliance is often evaluated on a quarterly cycle using running annual averages. Compliance cycles are set in each contaminant's specific subpart of 40 CFR Part 141; systems violate an MCL if their running average exceeds the standard during the applicable compliance period.

Cross-Connection — Any physical connection between a public water supply and a source of contamination, where water could flow in either direction depending on pressure. Backflow from a cross-connection can introduce contaminants into the distribution system. CCRs often reference cross-connection control programs in the source water section. State primacy agencies typically set cross-connection control requirements separately from the federal CCR rule.

CWS vs. PWS — A community water system (CWS) is a subset of public water systems that serves at least 25 year-round residents or 15 year-round service connections. Only CWSs are required to produce CCRs. See the full entry for the distinction between CWSs, non-transient non-community systems, and transient systems.

D

DBP (Disinfection Byproduct) — Chemical compounds formed when disinfectants such as chlorine react with naturally occurring organic matter in source water. The two primary DBP families regulated in CCRs are total trihalomethanes (TTHM) and haloacetic acids (HAA5). DBP levels are reported in CCRs as running annual averages; systems serving 10,000 or more people apply locational running annual averages (LRAA) under the Stage 2 D/DBPR. See 40 CFR Part 141 Subpart L and Subpart V.

Disinfectant Residual — The concentration of active disinfectant (chlorine, chloramines, or chlorine dioxide) maintained in treated water as it travels through the distribution system. Maintaining a residual is required to prevent microbial regrowth after treatment. CCRs report disinfectant residual levels against the Maximum Residual Disinfectant Level (MRDL); residual testing failures can trigger a treatment technique violation. See 40 CFR § 141.65.

E

EPA (U.S. Environmental Protection Agency) — The federal agency that sets and enforces national primary drinking water regulations under the Safe Drinking Water Act, including the CCR rule at 40 CFR Part 141 Subpart O (§§ 141.151–141.156). In states with primacy, EPA oversees state implementation. EPA publishes CCR guidance, sample reports, and compliance tools at epa.gov/ccr.

F

Finished Water — Drinking water that has completed all treatment steps and is ready for distribution to consumers. Finished water sampling is distinct from source water or in-process sampling and is the basis for MCL compliance determinations for most contaminants. The term appears in CCRs when distinguishing between where in the treatment process a sample was collected.

G

Groundwater Under the Direct Influence of Surface Water (GWUDI) — A groundwater source that has a significant potential for surface water contamination, typically demonstrated by the presence of microorganisms, turbidity, or other indicators linked to nearby surface water. GWUDI sources must meet surface water treatment requirements rather than groundwater rules. CCRs for systems using GWUDI sources must reflect the surface water treatment technique requirements. See 40 CFR § 141.2 for the regulatory definition.

H

Hazard Index (PFAS) — A unitless mixture metric used under EPA's 2024 PFAS National Primary Drinking Water Regulation to regulate combinations of four PFAS — PFHxS, PFNA, HFPO-DA (GenX Chemicals), and PFBS — when no individual MCL is exceeded. The MCL for the Hazard Index is 1. Note that PFBS has no individual MCL; it is regulated only through the Hazard Index. See the full entry for the calculation method.

L

LCR vs. LCRR vs. LCRI — Three successive versions of EPA's lead and copper regulation: the original Lead and Copper Rule (1991), the Lead and Copper Rule Revisions (LCRR, 2021), and the Lead and Copper Rule Improvements (LCRI, 2024). Each tightened requirements for action levels, sampling protocols, and service line replacement. Compliance with the LCRI begins November 1, 2027. See the full entry for the timeline and what changed in each iteration.

Lead Service Line (LSL) — A service line constructed of lead that runs from the water main to the building entrance, or to the meter if the meter is located at the building entrance. Under the LCRI (effective November 1, 2027), water systems must replace all lead service lines under their ownership or control within 10 years. CCRs must include a statement that a service line inventory has been prepared and instructions for customers to access it. See 40 CFR § 141.153(h)(8).

LCRR (Lead and Copper Rule Revisions) — The 2021 update to EPA's lead and copper regulations that established initial lead service line inventory requirements (initial inventory due October 16, 2024), updated tap sampling protocols including paired first- and fifth-liter sampling, and set groundwork for the more comprehensive LCRI that followed. See /ccr/glossary/lcr-vs-lcrr-vs-lcri/.

LCRI (Lead and Copper Rule Improvements) — The 2024 final rule (89 FR 86416, effective October 30, 2024) that lowered the lead action level from 15 µg/L to 10 µg/L, required paired first- and fifth-liter tap sampling with the higher value used for compliance, and mandated full replacement of all lead service lines within 10 years of the November 1, 2027 compliance date. See /ccr/glossary/lcr-vs-lcrr-vs-lcri/.

LRAA (Locational Running Annual Average) — A compliance metric used under the Stage 2 Disinfectants and Disinfection Byproducts Rule to calculate TTHM and HAA5 averages at each individual monitoring location, rather than averaging across the distribution system. Required for systems that conduct monitoring at multiple sites. See the full entry for how LRAA differs from RAA and which systems must use it.

M

MCL (Maximum Contaminant Level) — The highest concentration of a contaminant that is legally permitted in public drinking water. MCLs are enforceable standards set under the Safe Drinking Water Act. When a system exceeds an MCL, it is in violation and must notify customers and take corrective action. See the full entry for how MCLs are set and how they relate to MCLGs.

MCLG (Maximum Contaminant Level Goal) — A non-enforceable public health goal set at the level where no known or anticipated adverse health effects occur, with an adequate margin of safety. MCLGs for carcinogens and lead are set at zero. The MCLG is the science-based target; the MCL is the enforceable standard set as close to the MCLG as is technically and economically feasible. See the full entry.

MFL (Million Fibers per Liter) — The unit used to report asbestos concentration in drinking water. EPA's MCL for asbestos is 7 MFL (for fibers longer than 10 micrometers). Asbestos is a regulated contaminant under 40 CFR § 141.62 and must be reported in CCRs if detected or if a monitoring violation occurred.

Monitoring — The systematic sampling and analysis of drinking water to determine whether contaminant levels comply with MCLs, action levels, and treatment technique requirements. CCRs must summarize monitoring results for the reporting year. A monitoring violation — failing to collect required samples on schedule — is itself a reportable violation that must appear in the CCR, separate from any MCL exceedance.

MRDL (Maximum Residual Disinfectant Level) — The highest concentration of a disinfectant allowed in drinking water at the point of delivery to consumers. Separate MRDLs apply to chlorine (4.0 mg/L), chloramines (4.0 mg/L), and chlorine dioxide (0.8 mg/L). CCRs report disinfectant residual levels against the applicable MRDL. See the full entry.

N

Non-Detect (ND) — A laboratory result indicating that a contaminant was not detected above the method detection limit. CCRs typically show "ND" or "BDL" (below detection limit) in place of a numeric value when a contaminant was tested but not found above the detection threshold. See the full entry for how ND interacts with MCL compliance and how to read it on a CCR table.

NTU (Nephelometric Turbidity Unit) — The unit used to measure turbidity, or water cloudiness, caused by suspended particles. EPA's surface water treatment technique requires finished water turbidity to remain below 0.3 NTU in 95 percent of samples each month, and never exceed 1 NTU. CCRs report turbidity results for surface water and GWUDI systems; turbidity treatment technique violations must be disclosed. See 40 CFR § 141.173.

P

PHG (Public Health Goal) — A California-specific non-enforceable concentration level for contaminants in drinking water, set by the California Office of Environmental Health Hazard Assessment (OEHHA) to protect public health with no adverse effects at a lifetime of exposure. PHGs are used by the State Water Resources Control Board when setting CA MCLs. CA water systems include PHGs alongside federal MCLGs in their CCRs. See the full entry.

Primacy Agency — A state (or tribal) environmental or health agency that has received authority from EPA to implement and enforce the Safe Drinking Water Act's primary drinking water regulations within its jurisdiction. Most states have primacy; EPA directly implements the program in the handful of states and territories that do not. Primacy agencies can set standards stricter than federal minimums but not looser. See 40 CFR § 141.151(f) and EPA's primacy page.

PWSID (Public Water System Identification Number) — A unique identifier assigned by EPA and state primacy agencies to every regulated public water system. Format: two-letter state code followed by seven digits (e.g., CA0710010). PWS IDs appear in CCRs, EPA databases, and state compliance records, and are the primary key for cross-referencing monitoring data, violations, and system characteristics in federal and state systems.

R

RAA (Running Annual Average) — A compliance averaging method that calculates a contaminant's average concentration using the most recent four consecutive quarters of monitoring data, updated each time a new quarter is added and the oldest dropped. RAA is used for most disinfection byproduct MCL compliance determinations. See the full entry for the distinction between RAA and LRAA.

S

Sanitary Survey — A periodic inspection of a water system's physical infrastructure, operations, monitoring, and management conducted by the primacy agency or a certified third party. Sanitary survey findings can trigger required corrective actions. CCRs for surface water systems and GWUDI systems must include the date of the most recent sanitary survey and any significant deficiencies identified. See 40 CFR § 141.153(i).

SDWA (Safe Drinking Water Act) — The federal law (42 U.S.C. §§ 300f et seq.) that authorizes EPA to set national drinking water standards and requires public water systems to monitor, treat, and report on drinking water quality. The CCR requirement comes from SDWA § 1414(c)(4), added by the 1996 SDWA amendments and further modified by the America's Water Infrastructure Act of 2018. The current CCR rule lives at 40 CFR Part 141 Subpart O (§§ 141.151–141.156).

Source Water — The raw water drawn from rivers, lakes, reservoirs, groundwater aquifers, or other sources before it enters the treatment system. CCRs must include a brief description of the water source and, where available, a summary of the system's source water assessment results and any significant potential sources of contamination identified. See 40 CFR § 141.153(b).

T

Tier 1 / Tier 2 / Tier 3 Public Notification — Three tiers of public notice required when a water system has a violation or situation posing potential health risks, distinguished by urgency. Tier 1 (acute health risk, e.g., E. coli MCL violation) requires notification within 24 hours. Tier 2 (non-acute violation) requires notification within 30 days. Tier 3 (monitoring/reporting violations, other non-health situations) requires annual notice, which can be delivered in the CCR itself. See 40 CFR Part 141 Subpart Q.

Treatment Technique (TT) — A required process or operational procedure used in lieu of a numerical MCL when a contaminant cannot be reliably or cost-effectively measured in finished water, or when the treatment process itself is the most effective safeguard. Examples include filtration and disinfection requirements for surface water and GWUDI systems, and the corrosion control requirements for lead and copper. See the full entry.

TT Violation — A failure to meet a treatment technique requirement. Unlike MCL violations (which are determined by sample results), a TT violation occurs when a system fails to install or properly operate the required treatment process. Turbidity treatment technique violations, disinfection byproduct precursor removal failures, and unresolved corrosion control deficiencies are among the TT violations that must be reported in a CCR.

Turbidity — A measure of water cloudiness caused by suspended particles (sediment, algae, microorganisms). Turbidity is controlled through treatment techniques, not a numerical MCL. High turbidity can interfere with disinfection effectiveness and is a treatment indicator for surface water systems. CCRs report turbidity levels in NTU and note any treatment technique violations. See 40 CFR § 141.173 and the NTU entry above.

U

UCMR (Unregulated Contaminant Monitoring Rule) — An EPA program requiring large water systems to monitor for contaminants that are not yet regulated but may pose public health risks, generating the data EPA needs to make regulatory decisions. UCMR5 (2021–2025) required monitoring for PFAS; results from UCMR5 informed the 2024 PFAS NPDWR. Systems with UCMR5 results above health advisory levels may choose to reference those results in their CCRs. See EPA's UCMR page.

Units of Measurement (ppm, ppb, ppt, ng/L, pCi/L) — The concentration units used in CCR tables vary by contaminant and regulation. Parts per million (ppm) equals milligrams per liter (mg/L); parts per billion (ppb) equals micrograms per liter (µg/L); parts per trillion (ppt) equals nanograms per liter (ng/L), which is the unit for PFAS MCLs. Picocuries per liter (pCi/L) measures radioactive contaminants. See the full entry for conversion reference and which unit applies to which contaminants.

V

Variance — An authorization granted by a primacy agency allowing a water system to temporarily use an alternative treatment method or exceed an MCL, typically based on a determination that the system cannot afford compliance technology and that a variance is in the public interest. Variances must be disclosed in the CCR, along with the terms of the variance and the schedule for achieving compliance. See 40 CFR § 141.153(d)(9) and 42 U.S.C. § 300g-4.

W

Wholesale System — A public water system that provides drinking water to one or more other public water systems rather than directly to individual customers. Wholesale systems must provide monitoring data to their retail purchasers by April 1 each year so the retail systems can meet the July 1 CCR deadline. The retail system is ultimately responsible for producing the CCR; the wholesale system is responsible for supplying the underlying data. See 40 CFR § 141.152(d).

Last reviewed: 2026-05-03. Next scheduled review: every 6 months or after EPA glossary updates.