🧪 Disinfection byproducts

HAA5 Contamination Map

HAA5 are haloacetic acids that form when chlorine used to disinfect drinking water reacts with naturally occurring organic matter. They're colorless, odorless, and linked to increased cancer risk with long-term exposure. See how every state compares against the 60 µg/L EPA limit.

Cities exceeding 60 µg/L EPA limit

4,333

Cities with HAA5 testing data

60 µg/L

EPA maximum contaminant level (MCL)

2018–2020

UCMR 4 monitoring period powering this map

0%10%25%40%55%+ No data

Percentage of tested cities exceeding the EPA HAA5 maximum contaminant level

⚠

HAA5 are an unavoidable tradeoff of disinfection. Chlorinating water kills pathogens that historically caused mass disease outbreaks — but it also produces disinfection byproducts including HAA5. Managing DBPs means balancing two real risks: the immediate danger of microbial contamination against long-term chemical exposure.

HAA5 contamination: key numbers

60 µg/L

EPA maximum contaminant level for the HAA5 mixture — unchanged since the 1998 Stage 1 DBP Rule

0 µg/L

EPA maximum contaminant level goal (MCLG) for dichloroacetic acid (DCAA) — classified as a probable human carcinogen

4,900

Public water systems required to test for HAA5 under EPA's UCMR 4 program (2018–2020)

Haloacetic acid species regulated together: monochloroacetic, dichloroacetic, trichloroacetic, monobromoacetic, and dibromoacetic acids

Summer

Peak season for HAA5 formation — warm temperatures and high organic runoff increase byproduct formation

90–99%

HAA5 removal rate achievable with reverse osmosis — the most effective point-of-use treatment

States ranked by HAA5 exceedance rate

Percentage of tested cities where the running annual average HAA5 concentration exceeds the 60 µg/L EPA MCL. Data from EPA UCMR 4 (2018–2020). States with no UCMR 4 data are not shown.

#	State	Cities exceeding	Cities tested	Exceedance rate	Avg HAA5 (µg/L)
1	Oklahoma	4	58	7%	26.4
2	Colorado	1	64	2%	20.1
3	Louisiana	1	63	2%	16
4	Mississippi	1	61	2%	9
5	North Carolina	2	119	2%	25.7
6	Alabama	1	109	1%	16.6
7	Florida	2	187	1%	17.2
8	Kentucky	1	93	1%	29.4
9	New Jersey	2	309	1%	12
10	Pennsylvania	1	128	1%	19.9
11	Tennessee	1	123	1%	23.2
12	Texas	4	298	1%	15.7
13	Virginia	1	68	1%	22.8
14	AP	0	21	0%	21.5
15	Alaska	0	11	0%	13.4
16	Arizona	0	65	0%	5.9
17	Arkansas	0	60	0%	20.2
18	California	0	339	0%	9
19	Connecticut	0	110	0%	27.3
20	Delaware	0	11	0%	14.6

Understanding HAA5 in drinking water

What are HAA5?

HAA5 refers to five haloacetic acids regulated together: monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), monobromoacetic acid (MBAA), and dibromoacetic acid (DBAA). They are disinfection byproducts — compounds that form unintentionally when chlorine-based disinfectants react with naturally occurring organic matter in source water. They are colorless, odorless, tasteless, and undetectable without laboratory testing.

Health effects

The EPA classifies DCAA as a probable human carcinogen (Group B2) and TCAA as a possible human carcinogen (Group C). Long-term exposure above the MCL is associated with increased risk of bladder and colorectal cancer. Animal studies link high-dose DCAA and TCAA exposure to reproductive toxicity and developmental harm. Infants fed formula made with tap water receive proportionally higher DBP doses relative to body weight than adults.

Why surface water systems are highest risk

HAA5 formation depends on the amount of natural organic matter (NOM) in source water, the chlorine dose applied, water temperature, and distribution system residence time. Surface water systems — rivers, lakes, reservoirs — carry higher organic loads from soil and vegetation runoff. Agricultural regions see spikes after planting and harvest seasons. Water at the far end of long distribution systems can have measurably higher HAA5 than water leaving the treatment plant.

EPA regulation

The EPA regulates HAA5 under the Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules. The current MCL is 60 µg/L as a running annual average at each monitoring location. The Stage 2 DBP Rule (2006) tightened compliance by requiring monitoring at the highest-DBP locations in the distribution system — the locational running annual average (LRAA) — rather than averaging across all sites.

Reducing HAA5 exposure

Reverse osmosis systems remove 90–99% of HAA5 and are the most effective point-of-use option (NSF/ANSI 58). Activated carbon block filters certified under NSF/ANSI 53 remove 50–90% and are a practical under-sink option. Granular activated carbon provides 30–70% removal. Boiling water does not remove HAA5 — it may concentrate it by evaporation. Standard pitcher filters vary widely; verify NSF 53 certification before buying.

About this data

This map uses data from the EPA's UCMR 4 monitoring program (2018–2020), which required approximately 4,900 public water systems to test for HAA5 and related compounds. The program covered systems serving 10,000+ people, plus a statistical sample of smaller systems. Cities without UCMR 4 data are not reflected — they may have current compliance data in their Consumer Confidence Reports.

Frequently asked questions

Is HAA5 in tap water dangerous?

HAA5 are associated with increased cancer risk and reproductive effects at chronic exposure levels above the 60 µg/L MCL. Below the limit, individual risk is low — but long-term cumulative exposure is a legitimate concern, particularly for infants, pregnant women, and people whose tap water is consistently near the upper end of the limit. DCAA, one of the five regulated species, has an MCLG of zero because EPA considers any exposure to carry some cancer risk.

Does boiling water remove HAA5?

No — boiling does not remove HAA5 and may actually increase concentrations by reducing water volume through evaporation. Use activated carbon filtration (NSF/ANSI 53) or reverse osmosis (NSF/ANSI 58) for effective HAA5 reduction.

Why are HAA5 levels higher in summer?

Higher water temperatures accelerate the chemical reaction between chlorine and organic matter. Summer also brings increased agricultural runoff, algae growth, and higher organic loads in source water — all of which produce more HAA5 when chlorinated. Systems with long distribution networks see the highest summer peaks as water ages in pipes.

If my city isn't on this map, is my water safe?

Absence from this map means your water system wasn't covered by the UCMR 4 monitoring program — not that your water is HAA5-free. Check your utility's most recent Consumer Confidence Report (CCR), which must disclose HAA5 and TTHM levels annually. You can also request detailed results directly from your utility.

Check HAA5 levels in your city

Search for your city to see HAA5 concentrations, whether your utility exceeds the EPA limit, and filter recommendations for your water supply.

Search your city