Disinfection byproducts — TTHM, HAA5, bromate, chlorite.
The federal Disinfection Byproducts framework spans two subparts of 40 CFR 141. Stage 1 DBPR (Subpart L, §§ 141.130–141.135) sets MCLs for TTHM and HAA5 and MRDLs for disinfectants. Stage 2 DBPR (Subpart V, §§ 141.620–141.629) layers locational running annual average (LRAA) compliance at distribution system sites. Every CCR must disclose DBP detections and the MCL/MCLG for each regulated byproduct under § 141.153(d)(4).
Verified against eCFR § 141.64 on 2026-04-18.
Disinfection byproduct MCLs are codified in Subpart G (§ 141.64). Monitoring, compliance, and treatment-technique rules live in Subparts L and V. Click through for the authoritative text.
Bromate and chlorite MCLs and their compliance-determination methods are in § 141.64(a). We do not publish bromate/chlorite numeric values on this page — the compliance table has nuance around running annual averages that is best read directly from the eCFR.
§§ 141.130–141.135.
Stage 1 DBPR is the foundation for DBP compliance. TTHM and HAA5 running-annual-average compliance, disinfectant residual MRDLs, and TOC-removal treatment technique for surface water systems.
General requirements
Purpose and applicability of Stage 1 DBPR. Covers community water systems and non-transient non-community water systems that add a disinfectant (other than UV) or deliver water that has been disinfected.
Read on eCFR →Analytical requirements
Approved analytical methods for TTHM, HAA5, bromate, chlorite, chlorine, chloramine, chlorine dioxide, total organic carbon (TOC), and specific UV absorbance (SUVA).
Read on eCFR →Monitoring requirements
Sampling schedules and locations for TTHM, HAA5, bromate (systems using ozone), chlorite (systems using chlorine dioxide), TOC, and disinfectant residuals.
Read on eCFR →Compliance requirements
Running annual average calculation and reporting for MCL and MRDL compliance determinations under Stage 1.
Read on eCFR →Reporting and recordkeeping requirements
Quarterly or annual reporting to the primacy agency. Record retention for sampling results, system operation reports, and compliance determinations.
Read on eCFR →Treatment technique for control of DBP precursors
TOC removal requirements for subpart H (surface water) systems using conventional filtration treatment. Step 1 and Step 2 enhanced-coagulation percent-removal matrices by source-water TOC and alkalinity.
Read on eCFR →§§ 141.620–141.629 — LRAA compliance at IDSE sites.
Stage 2 tightens the DBPR by requiring compliance at specific locational running annual average (LRAA) sites selected through the Initial Distribution System Evaluation (Subpart U). It is additive to Subpart L, not a replacement.
General requirements
Purpose, applicability, and compliance-date schedule for Stage 2 DBPR. Governs locational running annual average (LRAA) compliance at distribution system sites.
Read on eCFR →Routine monitoring
Routine LRAA monitoring locations selected by an Initial Distribution System Evaluation (IDSE) under Subpart U, with frequency determined by system size and source type.
Read on eCFR →Subpart V monitoring plan
Required monitoring plan content — sampling locations, frequency, sample collection protocols, and the rationale for each site.
Read on eCFR →Reduced monitoring
Eligibility criteria for reduced sampling frequency after a system demonstrates stable compliance at Stage 2 LRAA sites.
Read on eCFR →Additional requirements for consecutive systems
Special provisions for consecutive systems that receive treated water from a wholesaler — notification, coordinated monitoring, and joint compliance determinations.
Read on eCFR →Conditions requiring increased monitoring
Triggers that bump a system from reduced back to routine or increased monitoring, including LRAA exceedances and significant operational changes.
Read on eCFR →Operational evaluation levels
Operational evaluation requirement when TTHM or HAA5 running-average exceeds the operational evaluation level at any LRAA site. Evaluation must identify the cause and planned mitigation.
Read on eCFR →Requirements for remaining on reduced TTHM and HAA5 monitoring
Conditions under which a system can remain on reduced monitoring based on its Subpart L results.
Read on eCFR →Requirements for increased TTHM and HAA5 monitoring
Conditions under which a system must return to increased monitoring based on its Subpart L results.
Read on eCFR →Reporting and recordkeeping requirements
Reporting to the primacy agency for Stage 2 LRAA compliance determinations, monitoring-plan updates, and operational evaluation submittals.
Read on eCFR →DBPs in your Consumer Confidence Report.
Every CCR that detects a DBP must disclose the detection level, range, sampling date, likely source, and the MCL/MCLG in the detected-contaminants table (§ 141.153(d)(4)). TTHM and HAA5 are the most commonly-reported DBPs. See our Consumer Confidence Report guide for the section-by-section walkthrough, or draft your own on the CCR Agent.
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