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Haloacetic Acids (HAA5) and Total Trihalomethanes (TTHM) in Drinking Water

Find maximum contaminant levels, health effects, monitoring and other requirements that public water systems must follow for haloacetic acids and total trihalomethanes – disinfection byproducts.

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Disinfection Byproducts - Haloacetic Acids and Trihalomethanes

Haloacetic acids and trihalomethanes are two groups of water disinfection byproducts, formed when chlorine or other disinfectants used to kill pathogenic organisms react with naturally occurring organic matter.

Maximum Contaminant Levels

Public water systems (PWS) must adhere to requirements for maximum contaminant levels (MCLs).

Contaminant MCL (mg/L)
Haloacetic acids (HAA5) 0.060
Total trihalomethanes (TTHM) 0.080

Compliance for TTHMs and HAA5s is determined based on a locational running annual average (LRAA) of quarterly sampling at each sample location in the distribution system.

Locational Running Annual Average equation for TTHM and HAA5

Each sample location will have its own LRAA. If the LRAA for any site exceeds the MCL, the PWS must notify customers about the violation as soon as possible but no later than 30 days after the violation is identified.

Monitoring, Sampling, and Analysis

PWSs can protect their customers from long-term health risks by regularly monitoring levels of TTHMs and HAA5s. Every PWS in Texas must allow for sampling of chemical contaminants. Unlike sampling for lead and copper, water quality parameters, microbes (coliform and E. coli), and disinfectant residuals-TCEQ uses contractors to collect samples for TTHMs and HAA5s.

TCEQ pays for the sample collection, and each PWS is responsible for paying the laboratory for the sample analysis. Samples are analyzed by the Lower Colorado River Authority (LCRA) or the Department of State Health Services (DSHS).

Sample Results

Texas Drinking Water Viewer (DWV) - Find monitoring schedules, sample locations, and results.

  • Instructions for Texas DWV - Under Samples click on Chemical Samples. Under Analyte Groups select DBP2 - DBP Phase 2. You can also filter by Collection Date or Sampling Point Type.

Sample Sites

Sample sites should be at a location or in an area where TTHMs and HAA5s have the highest potential for forming. In most cases these sites were designated by the system using the Initial Distribution System Evaluation and should not be changed except in a few distinct circumstances:

  • Water flow or water age has changed within the distribution system.
  • A new plant, source, or entry point has come on-line.
  • A customer refuses to allow water system personnel to collect samples.
  • Sample site is at a dead end main.

Before submitting a request to change a site, PWS personnel must evaluate the distribution system to identify locations that have the potential to form increased TTHM and HAA5 levels.

Consider the causes of TTHM and HAA5 formation:

Submit the change request to DBP@tceq.texas.gov at least two weeks before sampling. Include the reason or reasons for the site change and why you have selected this new site. If you do not notify TCEQ about the change, you may receive a monitoring and reporting violation.

Health Effects

An MCL exceedance of TTHMs or HAA5s is not an emergency. However, some people who drink water containing these contaminants may have an increased risk of liver, kidney, central nervous system damage or cancer. PWSs that exceed the MCL must identify options to reduce TTHM and HAA5 levels in their water.

Operational Evaluations

Operational Evaluations for Disinfection Byproducts in Drinking Water - The operational evaluation helps PWSs proactively identify high TTHM or HAA5 levels and act to decrease levels to avoid a MCL violation.

Consumer Notification

Public Notice Language for Drinking Water Compliance - Required language and certificate of delivery documents organized by contaminant to use for public notification if your PWS has a MCL or monitoring and reporting violation.

Consumer Confidence Report - Community water systems must provide the minimum, maximum, and average levels of any contaminant detected in their annual Consumer Confidence Report to customers by July 1 of each year. A community water system supplies water to the same population year-round.

Assistance and Tools for Public Water Systems

Contact the TCEQ DBP compliance coordinator at DBP@tceq.texas.gov or 512-239-1062 if you have questions about how to calculate the LRAA, find sample schedules, and sample results.

Find specific rule requirements for TTHMs and HAA5s in RG-346 Standards and Reporting Requirements for PWS. 

TCEQ Drinking Water Advisory Workgroup YouTube video - Information about types of DBPs, TTHM and HAA5 MCLs, operational evaluations, prevention, and treatment.

EPA Stage 2 Disinfectants and Disinfection Byproducts Rule Operational Evaluation Guidance Manual - Information about specific factors that influence DBP formation and ways to control formation can be found in this EPA guidance.

Financial, Managerial, and Technical Assistance - TCEQ offers FREE financial, managerial, and technical (FMT) assistance to help public water systems comply with regulations. Contact FMT for help with issues such as, but not limited to preventing operational problems, training about how to comply with rule requirements and performing capacity assessments.

Courtesy Compliance Reminders for Public Water System Operators - Sign up for text or email reminders about important public water system compliance requirements and deadlines. 

Technical Guidance for Public Water System Operators and Engineers - Information about technical questions, such as submitting plans, exploring treatment options, or requesting exceptions to design or capacity rules.

Operating a Public Water System - Information about how to operate a public water system, drinking water quality requirements, and reporting requirements.