40 CFR Part 141, subpart by subpart.
40 CFR Part 141 is the federal National Primary Drinking Water Regulation, enacted under the Safe Drinking Water Act. Every enforceable MCL, monitoring schedule, public notification tier, and Consumer Confidence Report (CCR) requirement lives here. This page maps every subpart to its authoritative eCFR page.
23 active subparts under Part 141.
Subpart letters are stable federal citations. When a state primacy agency adopts federal rules by reference, it typically mirrors these letters. Each subpart below links to the eCFR, which is the authoritative version — we never paraphrase regulation text.
General
Applicability, definitions (community water system, non-transient non-community water system, public water system, PWSID), and the scope of Part 141.
Maximum Contaminant Levels
Enforceable federal Maximum Contaminant Levels (MCLs) for inorganic and organic chemicals, radionuclides, turbidity, and microbiological contaminants.
Monitoring and Analytical Requirements
Sampling schedules, analytical methods, and laboratory certification rules that drive monitoring plans for every regulated contaminant.
Reporting and Recordkeeping
General reporting to primacy agencies and record-retention obligations, including § 141.33 retention periods (3 years for action records, 5 years for bacteriological analyses, 10 years for chemical analyses and sanitary surveys).
Special Regulations, Including Monitoring
Regulations for specific classes of systems and contaminants that require treatment-technique controls beyond the general framework.
Maximum Contaminant Level Goals and Maximum Residual Disinfectant Level Goals
Non-enforceable health-based targets (MCLGs and MRDLGs). Consumer Confidence Reports must disclose both MCL and MCLG per § 141.153(c)(1).
NPDWRs — MCLs and MRDLs
The enforceable National Primary Drinking Water Regulation MCLs and Maximum Residual Disinfectant Levels (MRDLs). Includes § 141.61 synthetic organic contaminants and § 141.64 disinfection byproducts.
Filtration and Disinfection
Treatment-technique rules for surface water and GWUDI systems, including the Surface Water Treatment Rule family.
Control of Lead and Copper
Lead and Copper Rule (LCR) / Lead and Copper Rule Improvements (LCRI). Action levels, service-line inventory and replacement, tap sampling, corrosion control. LCR→LCRI transition window: Oct 30, 2024 – Nov 1, 2027 per § 141.81(a)(4)(i).
Use of Non-Centralized Treatment Devices
Rules that apply when point-of-entry or point-of-use treatment devices are used to achieve compliance.
Treatment Techniques
Treatment techniques that serve as the compliance standard when an MCL cannot feasibly be set, such as for acrylamide and epichlorohydrin.
Disinfectant Residuals, Disinfection Byproducts, and DBP Precursors
Stage 1 Disinfectants and Disinfection Byproducts Rule: MRDLs for chlorine/chloramine/chlorine dioxide, and baseline monitoring for TTHM, HAA5, bromate, and chlorite.
Consumer Confidence Reports
The federal CCR rule. Six sections (§§ 141.151–141.156) plus Appendix A. July 1 annual delivery; biannual for systems ≥ 10,000 persons under the 2024 revisions (89 FR 46012).
Enhanced Filtration and Disinfection — Systems Serving 10,000 or More
Long Term 1 Enhanced Surface Water Treatment Rule provisions applicable to larger subpart H systems.
Public Notification of Drinking Water Violations
Tier 1/2/3 public notification requirements when a violation occurs. CCRs reference Tier 2 and Tier 3 violations from the reporting year per § 141.153(f).
Ground Water Rule
Source-water assessment and treatment-technique rule for systems using ground water that may be under the direct influence of surface water.
Enhanced Filtration and Disinfection — Systems Serving Fewer Than 10,000
Long Term 1 Enhanced Surface Water Treatment Rule for smaller subpart H systems.
Initial Distribution System Evaluations
Companion evaluation framework that feeds Stage 2 DBP monitoring plan selection.
Stage 2 Disinfection Byproducts Requirements
Stage 2 DBPR — locational running annual average compliance for TTHM and HAA5 at distribution-system sites selected under Subpart U.
Enhanced Treatment for Cryptosporidium
Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). Cryptosporidium monitoring and bin classifications.
Aircraft Drinking Water Rule
Aircraft-specific public water system rules for air carriers.
Revised Total Coliform Rule (RTCR)
Total coliform and E. coli monitoring. Triggers assessment levels (Level 1/Level 2) that a CCR must disclose per § 141.153(h)(5).
Control of Per- and Polyfluoroalkyl Substances (PFAS)
PFAS National Primary Drinking Water Regulation. MCLs for PFOA, PFOS, PFHxS, PFNA, HFPO-DA, and a Hazard Index MCL for PFAS mixtures.
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