HAA5 Contamination

HAA5 in Connecticut Drinking Water

Ranked by average HAA5 concentration (µg/L) · UCMR 4 data (2018–2020) · Data from EPA SDWIS & UCMR

Cities Tested

Exceeds Limit

% Exceeds Limit

26.9 µg/L

State Avg

▼ 1% vs national

vs National

105

Health Violations

Analysis

HAA5 in Connecticut: what the data shows

Connecticut has 93 cities with HAA5 monitoring data from the EPA's UCMR 4 program (2018–2020). Haloacetic acids (HAA5) form when chlorine-based disinfectants react with natural organic matter in water. The state average is 26.9 µg/L — better than the 15.5 µg/L national average. No cities currently exceed the 60 µg/L EPA MCL. HAA5 is a group of five chlorinated and brominated acetic acids. Long-term exposure above the MCL is associated with increased cancer risk and adverse reproductive outcomes. The EPA classifies total HAA5 as a probable human carcinogen at elevated concentrations. Activated carbon filtration (especially granular or block carbon) is effective at reducing HAA5. Running water through a refrigerator filter or letting it sit in an open pitcher for 30 minutes also helps, as some HAA5 species are volatile. Boiling does not remove disinfection byproducts and may concentrate them.

Comparison

Cities exceeding 60 µg/L EPA MCL

Connecticut

0 of 93 cities

← ▼ 1% below national rate (better)

National avg

23 of 4342 cities

City Map

HAA5 data across Connecticut

Each dot is a city with UCMR 4 HAA5 testing data. Cities where average HAA5 exceeded the 60 µg/L EPA MCL are highlighted. Size reflects population served.

Worst Offenders

Top 10 cities by haa5 level in Connecticut

Highest HAA5 levels (µg/L)

All Cities

All Connecticut cities ranked by haa5 level

#	City	Level	Exceeds?	Violations	Grade
1	Uncasville	49.9 µg/L	No	1	A
2	Bridgeport	49.0 µg/L	No	2	C-
3	Fairfield	49.0 µg/L	No	2	C-
4	Redding	49.0 µg/L	No	2	C-
5	Shelton	49.0 µg/L	No	2	C-
6	Stratford	49.0 µg/L	No	2	C-
7	Newtown	49.0 µg/L	No	46	F
8	Greenwich	43.2 µg/L	No	5	F
9	Westport	42.5 µg/L	No	2	C-
10	Stamford	41.3 µg/L	No	4	F
11	Stonington	39.1 µg/L	No	6	B
12	Watertown	38.3 µg/L	No	11	D+
13	Darien	37.9 µg/L	No	7	F
14	Seymour	37.9 µg/L	No	2	D+
15	Beacon Falls	37.8 µg/L	No	3	C-
16	Wilton	36.9 µg/L	No	7	D
17	Norwalk	36.4 µg/L	No	7	D
18	New Canaan	36.2 µg/L	No	7	F
19	Bozrah	35.1 µg/L	No	13	B
20	Franklin	35.1 µg/L	No	13	B
21	Lisbon	35.1 µg/L	No	27	F
22	Norwich	35.1 µg/L	No	19	B-
23	Preston	35.1 µg/L	No	23	D+
24	Oxford	32.9 µg/L	No	6	B
25	Groton	32.7 µg/L	No	17	F
26	Montville	31.9 µg/L	No	143	F
27	Ledyard	31.6 µg/L	No	23	D+
28	Ansonia	29.3 µg/L	No	0	B+
29	Bethany	29.3 µg/L	No	4	C-
30	Woodbridge	29.3 µg/L	No	0	B+
31	East Hartford	28.9 µg/L	No	0	A-
32	Hartford	28.9 µg/L	No	0	A-
33	Rocky Hill	28.9 µg/L	No	1	B
34	Wethersfield	28.9 µg/L	No	0	A-
35	Windsor	28.9 µg/L	No	0	A-
36	Portland	28.9 µg/L	No	9	C
37	Branford	28.3 µg/L	No	0	A-
38	Derby	28.3 µg/L	No	0	B+
39	East Haven	28.3 µg/L	No	0	A-
40	Hamden	28.3 µg/L	No	0	A-
41	Milford	28.3 µg/L	No	0	B+
42	New Haven	28.3 µg/L	No	0	A-
43	North Branford	28.3 µg/L	No	25	F
44	Orange	28.3 µg/L	No	0	B+
45	West Haven	28.3 µg/L	No	0	B+
46	Wolcott	28.2 µg/L	No	18	F
47	Prospect	28.1 µg/L	No	1	C+
48	Waterbury	28.0 µg/L	No	14	C
49	Meriden	27.1 µg/L	No	4	C+
50	Harwinton	27.1 µg/L	No	5	D
51	Torrington	27.1 µg/L	No	3	B+
52	North Haven	26.2 µg/L	No	0	C-
53	Wallingford	25.9 µg/L	No	4	D
54	Waterford	25.2 µg/L	No	16	C-
55	New London	25.2 µg/L	No	0	C+
56	Cromwell	25.0 µg/L	No	1	B
57	Middletown	24.9 µg/L	No	11	D
58	Windsor Locks	24.2 µg/L	No	0	B-
59	Cheshire	24.1 µg/L	No	28	F
60	Plymouth	23.5 µg/L	No	18	C
61	Southington	22.7 µg/L	No	12	F
62	Glastonbury	22.3 µg/L	No	4	B+
63	Newington	21.8 µg/L	No	1	D
64	West Hartford	21.8 µg/L	No	0	B+
65	Berlin	21.4 µg/L	No	6	F
66	Bristol	20.8 µg/L	No	4	C+
67	South Windsor	20.5 µg/L	No	5	C
68	Manchester	20.5 µg/L	No	8	C
69	Danbury	19.5 µg/L	No	59	F
70	Bethel	19.5 µg/L	No	25	F
71	Brookfield	19.5 µg/L	No	135	F
72	Farmington	19.3 µg/L	No	3	D+
73	Clinton	19.2 µg/L	No	4	D+
74	Guilford	19.2 µg/L	No	20	D
75	Madison	19.2 µg/L	No	18	C+
76	Old Saybrook	19.2 µg/L	No	0	B-
77	Westbrook	19.2 µg/L	No	7	C+
78	Plainville	16.9 µg/L	No	4	C
79	Avon	16.3 µg/L	No	3	C+
80	Ellington	14.7 µg/L	No	0	B
81	Suffield	14.7 µg/L	No	1	C+
82	Tolland	14.7 µg/L	No	24	F
83	Stafford	14.7 µg/L	No	12	C
84	Mansfield	14.1 µg/L	No	85	F
85	Mashantucket	12.4 µg/L	No	7	B
86	East Windsor	11.7 µg/L	No	25	F
87	Enfield	11.7 µg/L	No	9	D
88	New Britain	9.7 µg/L	No	0	B-
89	Naugatuck	8.6 µg/L	No	1	A
90	Hampton	5.7 µg/L	No	1	B
91	Somers	2.6 µg/L	No	6	C+
92	East Lyme	1.9 µg/L	No	6	C
93	Granby	0.9 µg/L	No	3	C+

FAQ

Frequently asked questions about haa5 in Connecticut

What is HAA5 and why does it appear in Connecticut tap water?

HAA5 (haloacetic acids) are disinfection byproducts that form when chlorine reacts with naturally occurring organic matter in source water. They are a normal byproduct of the disinfection process that makes water safe to drink. No cities in Connecticut currently exceed the 60 µg/L EPA MCL. The state average is 26.9 µg/L.

How can I reduce HAA5 exposure from Connecticut drinking water?

Activated carbon filters (granular or block) effectively reduce HAA5. Refrigerator filters and under-sink carbon systems are convenient options. Unlike lead or PFAS, HAA5 levels can also be reduced by letting water stand in an open container, as some species evaporate. Boiling does NOT remove HAA5 and can concentrate them by reducing water volume.

Which Connecticut cities have the highest HAA5 levels?

The cities with the highest average HAA5 concentrations in Connecticut are: Uncasville (49.9 µg/L), Bridgeport (49.0 µg/L), Fairfield (49.0 µg/L), Redding (49.0 µg/L), Shelton (49.0 µg/L). Note: this data is from UCMR 4 testing (2018–2020) and may not reflect current levels.

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