If your annual water-quality report lists HAA5, it means your utility measured a group of five haloacetic acids that can form during drinking-water disinfection. The number homeowners usually need to know first is 60 µg/L, or approximately 60 ppb—EPA's Maximum Contaminant Level for HAA5.
But interpreting that number is not always as simple as comparing one test result with 60. EPA compliance is generally evaluated using a Locational Running Annual Average (LRAA), which accounts for results collected over time at individual monitoring locations.
This guide explains what HAA5 is, why it forms, how to read HAA5 results in your Consumer Confidence Report, what current research says about long-term exposure, and what to look for if you want additional at-home filtration.
Last reviewed: September 2026. This guide is educational and is not medical advice.
HAA5 in Drinking Water: The Quick Answer
What is HAA5?
A group of five regulated haloacetic acids that can form when drinking-water disinfectants react with naturally occurring organic material.
What is EPA's limit?
60 µg/L, equal to 0.060 mg/L and approximately 60 parts per billion.
Does one result above 60 ppb mean a violation?
Not necessarily. Compliance under the Stage 2 DBPR is generally based on a location's running annual average.
Can home filtration reduce HAA5?
Some treatment technologies may reduce haloacetic acids, but performance varies significantly. Look for HAA-specific performance evidence rather than assuming all carbon filters perform the same way.
What Is HAA5?
HAA5 does not refer to a single chemical.
It is the regulatory name for the combined concentration of five haloacetic acids:
When a Consumer Confidence Report says, for example, “HAA5: 38 ppb,” that normally represents the total concentration of these five regulated compounds rather than 38 ppb of one particular haloacetic acid.
Other haloacetic acids can also occur in treated water, but the five above are the compounds included in the current federal HAA5 standard.
How Do Haloacetic Acids Get Into Drinking Water?
HAA5 is generally classified as a group of disinfection byproducts, or DBPs.
Haloacetic acids can form when disinfectants used during water treatment react with naturally occurring organic matter in source water.
Organic material enters source water
Natural organic matter can come from vegetation and other material in rivers, reservoirs, and other water sources.
The water is treated and disinfected
A disinfectant is used as part of the utility's treatment process.
Chemical reactions occur
The disinfectant can react with remaining organic matter.
DBPs can form
These reactions can produce HAA5, TTHMs, and other disinfection byproducts.
Haloacetic acids are therefore usually not deliberately added to the water. They are created through chemical reactions associated with disinfection.
Why Do HAA5 Levels Change Throughout the Year?
HAA5 is not necessarily present at exactly the same concentration every day.
Formation can be affected by several variables:
- Water temperature
- The amount and type of natural organic matter
- Source-water conditions
- Disinfectant type and dose
- pH and other water chemistry
- Treatment practices
- Storage conditions
- Time spent in the distribution system
Warmer conditions can accelerate many chemical reactions involved in disinfection-byproduct formation. Seasonal changes in rainfall, reservoir conditions, source-water blending, and organic material can also influence HAA5 levels.
Water age can matter as well. Reactions can continue while treated water travels through storage tanks and distribution pipes.
That helps explain why one monitoring location may report a different HAA5 concentration from another location served by the same utility.
What Is EPA's Limit for HAA5?
EPA Maximum Contaminant Level for HAA5
The federal Maximum Contaminant Level for HAA5 is:
60 µg/L = 0.060 mg/L ≈ 60 ppb
These are simply different units expressing approximately the same concentration in water.
But compliance isn't based on one isolated sample
Under EPA's Stage 2 Disinfectants and Disinfection Byproducts Rule, compliance for HAA5 is generally determined using the Locational Running Annual Average, or LRAA.
Each compliance monitoring location is evaluated over time.
This is important because a single HAA5 measurement can be higher or lower than the water system's longer-term average.
The key compliance measurement is the LRAA for the individual monitoring location.
How to Read HAA5 in Your Consumer Confidence Report
If you receive water from a community water system, start with your utility's annual Consumer Confidence Report (CCR).
HAA5 may appear under headings such as:
- Disinfection Byproducts
- Regulated Contaminants
- Detected Contaminants
- Water Quality Results
The contaminant itself may be labeled:
- HAA5
- Haloacetic Acids
- Haloacetic Acids (Five)
- Total Haloacetic Acids
Example HAA5 water report
| Contaminant | Highest LRAA | Range | MCL | Violation? |
|---|---|---|---|---|
| HAA5 | 41 ppb | 18–57 ppb | 60 ppb | No |
Here's how to interpret this example:
- 41 ppb is the highest reported locational running annual average.
- 18–57 ppb represents the range of individual results presented by the utility.
- 60 ppb is EPA's Maximum Contaminant Level.
- The utility reports no violation.
Notice that the highest individual value in the range—57 ppb—is not necessarily the number used by itself to determine regulatory compliance.
What if you see an individual value above 60 ppb?
Before concluding that a violation occurred, determine what the number represents.
It could be:
- a single laboratory sample,
- a range maximum,
- a quarterly result,
- an Operational Evaluation Level, or
- the compliance LRAA.
If the report is unclear, ask the utility specifically:
“What was the HAA5 LRAA for the monitoring location serving my area, and was there an HAA5 MCL violation?”
What Does Current Research Say About HAA5 and Health?
EPA regulates HAA5 due to concerns about long-term exposure to disinfection byproducts.
EPA currently describes the potential health effect from consuming water containing HAA5 above the MCL over many years as an increased risk of cancer.
That statement should be interpreted carefully.
What it means
Long-term exposure to disinfection byproducts is an area of legitimate toxicological and epidemiological research, and the evidence was important in establishing drinking-water regulation.
What it doesn't mean
Detecting HAA5 in one glass of water—or seeing HAA5 listed in a compliant Consumer Confidence Report—does not mean an individual is expected to develop cancer.
Why studying HAA5 is complicated
Most people are not exposed to one haloacetic acid in isolation.
Disinfected drinking water can contain mixtures of:
- different haloacetic acids,
- trihalomethanes,
- other regulated DBPs, and
- many unregulated disinfection byproducts.
Human studies therefore frequently use HAA5, TTHM or another DBP measurement as an exposure indicator, rather than being able to isolate one individual molecule perfectly.
That makes cause-and-effect interpretation more difficult.
Dichloroacetic acid and trichloroacetic acid
Two members of HAA5—dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA)—have received considerable toxicological attention.
Animal studies using substantially higher experimental exposures have identified carcinogenic and other toxic effects for certain haloacetic acids. These studies help identify potential hazards and inform risk assessment, but experimental doses cannot simply be equated with the much lower concentrations normally measured in municipal drinking water.
What do human studies show?
Epidemiological research has examined possible associations between long-term exposure to drinking-water disinfection byproducts and cancer.
A systematic review and dose-response meta-analysis published in 2024 reported positive associations between increasing exposure to several DBP measures and cancer risk, including an association involving HAA5 exposure.
However, observational research has limitations. Exposure can be difficult to reconstruct over decades, people move between water systems, and HAA5 often occurs alongside other DBPs.
What About Pregnancy and Reproductive Health?
Researchers have also investigated disinfection byproducts in relation to pregnancy and birth outcomes.
Studies have examined outcomes including:
- birth defects,
- fetal growth,
- preterm birth, and
- other reproductive outcomes.
A 2025 systematic review and dose-response meta-analysis examined the association between DBP exposure and congenital anomalies, reflecting ongoing research interest in this area.
But reproductive studies can be particularly difficult to interpret because exposure estimates, DBP mixtures, population characteristics, confounding factors and study methods differ substantially.
It would therefore be inappropriate to turn this developing body of research into a simple statement that a particular HAA5 result predicts a pregnancy outcome.
If your utility has issued an HAA5 violation notice and you have a pregnancy-specific medical concern, discuss your individual situation with a qualified healthcare professional.
HAA5 vs. TTHMs: What's the Difference?
If your water report contains HAA5, there is a good chance you will also see TTHMs.
Both are major regulated classes of disinfection byproducts, but they are chemically different.
| HAA5 | TTHMs | |
|---|---|---|
| What it represents | Five haloacetic acids | Four trihalomethanes |
| EPA MCL | 60 ppb | 80 ppb |
| Formed during disinfection? | Yes | Yes |
| Volatility | Generally much less volatile | More volatile |
| Compliance approach | LRAA | LRAA |
This difference in volatility matters.
TTHMs can contribute to exposure not only through ingestion but also through inhalation and other routes associated with activities such as showering.
Haloacetic acids are much less volatile, so ingestion of drinking water is generally the more relevant household exposure pathway for HAA5.
For a detailed explanation, see our Trihalomethanes (TTHMs) in Drinking Water Guide.
Should You Test Your Tap Water for HAA5?
For most households receiving municipal water, the Consumer Confidence Report is the logical first step.
Your utility's compliance monitoring provides more information about long-term HAA5 behavior across the distribution system than one isolated homeowner sample.
Additional testing may be useful when you have a specific question, such as:
- You want to know the concentration at your own tap.
- Your utility recently reported elevated HAA5 results.
- You live near the end of a distribution system or in an area with long water residence times.
- You want to compare unfiltered and filtered water.
- You are evaluating a filtration system's real-world performance.
Use a qualified drinking-water laboratory
HAA5 is not a good candidate for an ordinary home test strip.
If you need a quantitative result, use a laboratory that offers appropriate haloacetic-acid analysis and follow its sampling instructions carefully.
If evaluating a filter, consider collecting:
Collecting paired samples under similar conditions can provide much more useful information than testing only the filtered water.
Can HAA5 Be Reduced With a Home Water Filter?
Potentially—but HAA5 filtration claims deserve more scrutiny than generic “carbon filter” claims.
Haloacetic acids have different chemical behavior from TTHMs. You should therefore not assume that a product shown to reduce chlorine or TTHMs automatically provides the same reduction for HAA5.
| Technology | What homeowners should know |
|---|---|
| Activated carbon | Carbon adsorption is widely used for many organic compounds and DBPs, but HAA performance can depend considerably on carbon type, system design, water chemistry, contact time, and individual haloacetic acid. Look for HAA-specific test data. |
| Reverse osmosis | Membrane systems can reduce a wide range of dissolved substances, but actual HAA performance varies by system. Review contaminant-specific performance information rather than relying solely on the term “reverse osmosis.” |
| Specialty treatment media | Some systems use adsorption or other media targeted toward organic contaminants. Performance evidence should identify the actual compounds tested. |
| Generic pitcher/refrigerator filter | Do not assume HAA5 reduction simply because the product contains activated carbon or reduces chlorine taste and odor. |
What should you look for before buying?
- Does the performance report specifically mention haloacetic acids, HAA5, DCAA, TCAA, MCAA, MBAA or DBAA?
- What concentrations were used during testing?
- How much reduction occurred?
- Was performance tested through the filter's rated service life?
- Was testing performed by an independent laboratory?
- What flow rate or contact time was used?
- How often does the filter need to be replaced?
Berkey® Systems and HAA5: What We Can—and Cannot—Say
Berkey® gravity-fed systems provide point-of-use countertop filtration for drinking and cooking water and are available in several capacities.
Manufacturer performance information for Black Berkey® Elements includes testing for a broad range of drinking-water contaminants and identifies trihalomethanes among the substances tested.
However, TTHM performance should not be presented as proof of HAA5 reduction.
HAA5 and TTHMs are both disinfection byproducts, but they have different chemical characteristics. Unless product documentation provides specific HAA or individual haloacetic acid performance results, homeowners concerned specifically with HAA5 should not assume that the TTHM results apply.
Review the current performance documentation for the filtration element you intend to use, and specifically look for HAA5 or individual haloacetic acids.
Choosing a Berkey® system for everyday drinking water
If you're considering a Berkey® system for broader point-of-use drinking water filtration, choose the system size based on your household's daily water needs.
| System | Capacity | Typical fit |
|---|---|---|
| Travel Berkey® | 1.5 gallons | 1–2 people or limited counter space |
| Big Berkey® | 2.25 gallons | Popular everyday household size |
| Royal Berkey® | 3.25 gallons | Larger households |
| Imperial Berkey® | 4.5 gallons | Higher daily water demand |
| Crown Berkey® | 6 gallons | Large households and shared spaces |
Compare Berkey® Water Filter Systems
If you already own a Berkey®, see the Berkey® Replacement Filters Guide for current element availability and compatibility.
What Should You Do If Your Water Report Shows HAA5?
Find the HAA5 entry.
Look under disinfection byproducts or regulated contaminants.
Confirm the units.
60 µg/L is equivalent to 0.060 mg/L and approximately 60 ppb.
Identify what the reported value represents.
Determine whether you're looking at an individual result, a range, an LRAA, or the Highest LRAA.
Check the violation column.
Do not conclude that one unusual result automatically represents regulatory noncompliance.
Ask the utility about your area if necessary.
HAA5 can vary among distribution-system monitoring locations.
If you want an additional reduction, evaluate evidence for HAA-specific filtration.
Do not assume chlorine or TTHM performance automatically establishes HAA5 performance.
Frequently Asked Questions About HAA5
What does HAA5 stand for?
HAA5 refers to five regulated haloacetic acids: monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid and dibromoacetic acid.
What is EPA's limit for HAA5?
EPA's Maximum Contaminant Level is 0.060 mg/L, which equals 60 µg/L and approximately 60 parts per billion.
Is HAA5 the same as chlorine?
No. Chlorine can be used as a disinfectant during water treatment. HAA5 refers to chemical byproducts that can form when disinfectants react with naturally occurring organic material.
Is HAA5 the same as TTHMs?
No. Both are regulated groups of disinfection byproducts, but HAA5 contains five haloacetic acids while TTHMs contain four trihalomethanes. EPA's current MCL is 60 ppb for HAA5 and 80 ppb for TTHMs.
Why does my water report show only one HAA5 number?
Because HAA5 is regulated as the combined concentration of five haloacetic acids. Utilities commonly report the total rather than displaying all five compounds individually.
Does one HAA5 test above 60 ppb mean my utility violated EPA rules?
Not necessarily. Stage 2 DBPR compliance is generally determined using a Locational Running Annual Average for each monitoring location. Check whether the value you see is an individual result, range maximum, LRAA or another measurement.
Why can HAA5 be higher during some parts of the year?
HAA5 formation can vary with temperature, natural organic matter, treatment conditions, source-water changes, water chemistry and distribution-system residence time. Seasonal variation is therefore common.
Can I taste or smell HAA5?
HAA5 at drinking-water concentrations should not be evaluated by taste or smell. A noticeable chlorine taste or odor does not tell you how much HAA5 is present.
Are HAA5 levels the same throughout my city?
Not necessarily. HAA5 can vary among monitoring locations because water age, temperature, source-water blending and other distribution-system conditions can differ.
Should I test my own tap water for HAA5?
Your utility's Consumer Confidence Report is generally the best first step. Laboratory testing may be useful if you want a tap-specific result, are investigating reported elevated levels, or want to compare unfiltered and filtered water.
Can activated carbon reduce HAA5?
Some carbon-based treatment systems may reduce certain haloacetic acids, but performance depends on the carbon, filter design, contact time, water chemistry and individual compound. Look for HAA-specific performance data rather than assuming all activated-carbon filters work equally well.
Does a filter that reduces TTHMs automatically reduce HAA5?
No. TTHMs and HAA5 are chemically different groups of disinfection byproducts. Performance testing for one group should not automatically be treated as performance evidence for the other.
Do Berkey® filters reduce HAA5?
Manufacturer information for Black Berkey® Elements includes TTHM testing, but TTHM performance should not be automatically extended to HAA5. If HAA5 is your specific concern, review current product documentation for testing that specifically identifies HAA5 or individual haloacetic acids.
Do private wells contain HAA5?
HAA5 is primarily associated with water that has undergone disinfection involving reactive disinfectants and organic material. A typical untreated private well does not have the same treatment process as a municipal system, although individual treatment systems can differ.
The Bottom Line
Seeing HAA5 on your Consumer Confidence Report does not, by itself, mean that something has gone wrong.
HAA5 is a group of disinfection byproducts that are routinely monitored and can form during treatment and as water moves through a distribution system.
The key federal number is:
60 µg/L ≈ 60 ppb
But don't evaluate your report using that number alone. Determine whether you are looking at an individual sample, a range, or the Locational Running Annual Average used for regulatory compliance.
Research into long-term DBP exposure continues, including research on cancer and reproductive outcomes. That is different from saying that simply detecting HAA5 at a compliant concentration predicts a health outcome for an individual household.
If you want to go beyond your utility's water treatment, choose home filtration based on contaminant-specific evidence. HAA5 and TTHMs are related as disinfection byproducts, but test results for one should not automatically be applied to the other.