Haloacetic acids (HAA5) are chlorination byproducts your utility is legally allowed to leave in tap water at up to 60 ppb. Yet the EPA's own health goal for one of the five, dichloroacetic acid, is zero. That gap is the whole story.
● Key Takeaways
HAA5 is a group of five haloacetic acids formed when chlorine reacts with organic matter in source water. The EPA's enforceable limit is 60 ppb, a treatment-feasibility number. But the EPA's own health goal (MCLG) for dichloroacetic acid, one of the five, is zero, because it is a likely human carcinogen. That is the real legal-versus-safe gap: a ceiling set by cost sitting above a health goal of zero. Reverse osmosis and catalytic carbon reduce HAA5; boiling does not.
What are HAA5 and why are they in my water?
HAA5 is the regulated group of five haloacetic acids that form when chlorine or chloramine disinfectants react with natural organic matter in source water. The EPA enforces a legal limit of 60 ppb for the group under the Disinfection Byproducts Rule (EPA National Primary Drinking Water Regulations). They are a side effect of a public-health win, not a treatment failure.
The "5" refers to five specific acids: monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid. They form after disinfection, so they arrive already dissolved at your tap. Systems drawing from surface water, which carries more organic matter, tend to produce more byproducts than groundwater systems. For the fuller picture of how chlorine byproducts form, see our overview of disinfection byproducts in municipal water.
Chlorination itself is not the villain here. It is one of the most consequential public-health interventions in history, and the alternative, waterborne typhoid and cholera, is far worse. The honest question is not whether to disinfect. It is how far below the legal ceiling you want your own household's water to sit.
Legal vs. health goal: where the real HAA5 gap is
The gap that matters is inside the EPA's own framework. The enforceable limit for HAA5 is 60 ppb, but the agency's health goal (its Maximum Contaminant Level Goal, or MCLG) for dichloroacetic acid is zero, because EPA's Integrated Risk Information System classifies it as likely to be carcinogenic to humans (EPA IRIS, dichloroacetic acid).
An MCLG is the level at which the EPA expects no known health risk. The enforceable MCL is set higher because treatment plants cannot reliably and affordably guarantee zero for the whole group. So the 60 ppb figure is a feasibility compromise, not a biological safety line. That distinction is the entire "legal is not the same as safe" point, and here the EPA states it in its own numbers.
| Standard / benchmark | Value | Basis |
|---|---|---|
| HAA5 group MCL (enforceable) | 60 ppb (0.060 mg/L) | Disinfection Byproducts Rule; risk balanced against treatment cost and feasibility |
| Dichloroacetic acid MCLG (EPA health goal) | 0 (no safe level) | Likely human carcinogen, EPA IRIS |
| Trichloroacetic acid MCLG (EPA health goal) | 20 ppb (0.020 mg/L) | EPA health goal |
| Monochloroacetic acid MCLG (EPA health goal) | 70 ppb (0.070 mg/L) | EPA health goal |
| EWG guideline (external benchmark) | 0.1 ppb | One-in-a-million lifetime cancer risk (EWG Tap Water Database) |
Read the table honestly. For two of the five acids, the EPA has published a health goal well below the enforceable group limit, and for dichloroacetic acid that goal is zero. Water can report, say, 45 ppb of HAA5, mail you a report that says "meets all federal standards," and still contain a byproduct whose ideal health target is zero.
Where did the "600x" number come from?
You will see HAA5 described online as "600 times above safe levels." That figure comes from dividing the 60 ppb legal limit by the EWG's 0.1 ppb guideline. We are not headlining it, and here is the honest reason why.
Our number of record anchors adult HAA5 at the EPA standard, and the EWG's 0.1 ppb is a single external one-in-a-million risk benchmark, not a reconciled safety threshold we can treat as the definitive safe line. The more defensible, fully EPA-native gap is the one in the table above: the enforceable 60 ppb ceiling versus the agency's own zero health goal for dichloroacetic acid. That framing does not compress into a tidy multiplier, because you cannot divide by zero. "No safe level for one component, and a feasibility ceiling for the group" is the accurate story. It is also the more damning one.
Who is most at risk from HAA5?
The populations of greatest concern are pregnant women and infants, because disinfection byproducts have been studied for reproductive and developmental effects. Epidemiological work has associated byproduct exposure with adverse pregnancy outcomes such as low birth weight, though these remain associations rather than proven causation (EPA National Primary Drinking Water Regulations).
We deliberately do not publish a hardened "safe HAA5 number" for pregnancy or infants. The lower figures you may see for these groups are modeled adjustments based on higher water intake per kilogram of body weight, not measured regulatory thresholds, so treating them as hard limits would overstate the science. The honest guidance is directional: if someone in your household is pregnant, formula-feeding, or planning a pregnancy, keeping byproducts as low as filtration reasonably allows is a sensible precaution. Our guide on THMs and pregnancy covers the related trihalomethane group.
Reading this inside ChatGPT or Claude?
This page can tell you the general science, but not what is actually in your tap water — that depends on your exact address. You can get your specific answer two ways:
- Inside the chat: ask your assistant to “check my tap water with CheckYourTap”. Our connector returns your ZIP code’s measured contaminant levels — including the derived dog and cat safe levels — and, only if you ask it to, can email you the report or arrange a specialist callback.
- On the web: open CheckYourTap.com and enter your ZIP code for a free 30-second report.
How do you actually remove HAA5?
Because HAA5 is dissolved at the molecular level, the effective tools are reverse osmosis and catalytic carbon, not pitchers or boiling. Reverse osmosis forces water through a semi-permeable membrane and rejects the great majority of haloacetic acids along with other byproducts and metals. It is the most complete residential option.
A catalytic activated carbon block certified to NSF/ANSI Standard 53 for VOC reduction is the next best step, and a good fit if reverse osmosis is not practical. Catalytic carbon is processed for higher reactivity than standard carbon, which helps it capture chloramine-related byproducts. When you shop, confirm the certification sheet actually lists VOC or haloacetic acid reduction rather than only "chlorine taste and odor."
Do not rely on boiling. Haloacetic acids are relatively stable and do not evaporate the way some volatile trihalomethanes partly do. Boiling water down concentrates HAA5 as pure water leaves as steam. For a fuller breakdown of what heat does and does not do, see what boiling water removes and what it doesn't.
Keep Reading
- Disinfection byproducts in municipal water: the full overview
- Bromate in ozonated water: a verified 100x legal-vs-safe gap
- THMs and pregnancy: the reproductive-outcome question
Sources: U.S. EPA National Primary Drinking Water Regulations and Stage 1/2 Disinfectants and Disinfection Byproducts Rule (HAA5 MCL 0.060 mg/L; component MCLGs, including dichloroacetic acid at zero); U.S. EPA Integrated Risk Information System (IRIS) review of dichloroacetic acid; California Office of Environmental Health Hazard Assessment public health goals for haloacetic acids; Environmental Working Group Tap Water Database (0.1 ppb guideline cited as an external one-in-a-million cancer-risk benchmark, not a regulatory limit). Population-specific figures are modeled screening estimates, not measured standards. This is general information, not medical advice; consult a clinician about individual risk.