HAA5 Contamination

HAA5 in Connecticut Drinking Water

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

110

Cities Tested

Exceeds Limit

% Exceeds Limit

27.3 µg/L

State Avg

▼ 1% vs national

vs National

134

Health Violations

Analysis

HAA5 in Connecticut: what the data shows

Connecticut has 110 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 27.3 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 110 cities

← ▼ 1% below national rate (better)

National avg

23 of 4420 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	Beacon Falls	49.0 µg/L	No	46	F
3	Beacon Falls	49.0 µg/L	No	7	F
4	Beacon Falls	49.0 µg/L	No	2	F
5	Beacon Falls	49.0 µg/L	No	2	F
6	Beacon Falls	49.0 µg/L	No	2	F
7	Beacon Falls	49.0 µg/L	No	2	C-
8	Beacon Falls	49.0 µg/L	No	2	C-
9	Beacon Falls	49.0 µg/L	No	2	C-
10	Beacon Falls	49.0 µg/L	No	2	C-
11	Beacon Falls	49.0 µg/L	No	2	C-
12	Beacon Falls	43.2 µg/L	No	5	F
13	Beacon Falls	42.5 µg/L	No	2	C-
14	Beacon Falls	41.3 µg/L	No	4	F
15	Beacon Falls	39.2 µg/L	No	27	F
16	Groton	39.1 µg/L	No	6	B-
17	Middlebury	38.3 µg/L	No	18	C-
18	Middlebury	38.3 µg/L	No	11	D+
19	Beacon Falls	37.9 µg/L	No	7	F
20	Ansonia	37.9 µg/L	No	2	D
21	Beacon Falls	37.8 µg/L	No	3	C-
22	Beacon Falls	36.9 µg/L	No	7	D
23	Beacon Falls	36.4 µg/L	No	7	D
24	Beacon Falls	36.2 µg/L	No	7	D
25	Franklin	35.1 µg/L	No	27	F
26	Franklin	35.1 µg/L	No	32	F
27	Franklin	35.1 µg/L	No	19	B-
28	Franklin	35.1 µg/L	No	23	D+
29	Franklin	35.1 µg/L	No	13	B
30	Franklin	35.1 µg/L	No	13	B
31	Ansonia	32.9 µg/L	No	6	B-
32	Groton	32.7 µg/L	No	17	F
33	Franklin	31.9 µg/L	No	143	F
34	Groton	31.6 µg/L	No	23	D+
35	Ansonia	29.3 µg/L	No	4	D+
36	Ansonia	29.3 µg/L	No	0	B+
37	Ansonia	29.3 µg/L	No	0	B+
38	Berlin	28.9 µg/L	No	9	C
39	Berlin	28.9 µg/L	No	33	F
40	Berlin	28.9 µg/L	No	1	B
41	Berlin	28.9 µg/L	No	0	A-
42	Berlin	28.9 µg/L	No	0	A-
43	Berlin	28.9 µg/L	No	0	A-
44	Berlin	28.9 µg/L	No	0	A-
45	Ansonia	28.3 µg/L	No	0	B+
46	Ansonia	28.3 µg/L	No	0	B+
47	Ansonia	28.3 µg/L	No	25	F
48	Ansonia	28.3 µg/L	No	0	B+
49	Ansonia	28.3 µg/L	No	0	B+
50	Ansonia	28.3 µg/L	No	0	B+
51	Ansonia	28.3 µg/L	No	0	B+
52	Ansonia	28.3 µg/L	No	0	B+
53	Ansonia	28.3 µg/L	No	0	B+
54	Ansonia	28.2 µg/L	No	18	F
55	Ansonia	28.1 µg/L	No	1	C+
56	Middlebury	28.0 µg/L	No	14	C
57	Ansonia	27.1 µg/L	No	4	C+
58	Harwinton	27.1 µg/L	No	8	F
59	Harwinton	27.1 µg/L	No	19	F
60	Harwinton	27.1 µg/L	No	3	B+
61	Harwinton	27.1 µg/L	No	5	D
62	Ansonia	26.2 µg/L	No	0	C-
63	Ansonia	25.9 µg/L	No	4	D
64	New London	25.2 µg/L	No	16	C-
65	New London	25.2 µg/L	No	0	C+
66	Berlin	25.0 µg/L	No	1	B-
67	Cromwell	24.9 µg/L	No	11	D
68	Cromwell	24.9 µg/L	No	25	F
69	Berlin	24.2 µg/L	No	0	B-
70	Ansonia	24.1 µg/L	No	28	F
71	Bristol	23.5 µg/L	No	18	C
72	Bristol	23.5 µg/L	No	9	C
73	Berlin	23.0 µg/L	No	40	F
74	Ansonia	22.7 µg/L	No	12	F
75	Berlin	22.3 µg/L	No	4	B+
76	Berlin	21.8 µg/L	No	1	D
77	Berlin	21.8 µg/L	No	0	B+
78	Berlin	21.4 µg/L	No	6	F
79	Bristol	20.8 µg/L	No	4	C+
80	Berlin	20.5 µg/L	No	5	C
81	Berlin	20.5 µg/L	No	8	C
82	Bethel	19.5 µg/L	No	135	F
83	Bethel	19.5 µg/L	No	59	F
84	Bethel	19.5 µg/L	No	25	F
85	Berlin	19.3 µg/L	No	3	D+
86	Clinton	19.2 µg/L	No	18	C+
87	Clinton	19.2 µg/L	No	20	D
88	Clinton	19.2 µg/L	No	4	D+
89	Clinton	19.2 µg/L	No	7	C+
90	Clinton	19.2 µg/L	No	0	B-
91	Windham	18.0 µg/L	No	11	B+
92	Berlin	16.9 µg/L	No	4	C
93	Plainville	16.3 µg/L	No	3	C+
94	East Granby	14.7 µg/L	No	24	F
95	East Granby	14.7 µg/L	No	12	C-
96	East Granby	14.7 µg/L	No	1	C+
97	East Granby	14.7 µg/L	No	0	B
98	East Granby	14.1 µg/L	No	85	F
99	East Granby	13.4 µg/L	No	5	C-
100	Mashantucket	12.4 µg/L	No	7	B
101	East Granby	11.7 µg/L	No	9	D
102	East Granby	11.7 µg/L	No	25	F
103	Berlin	9.7 µg/L	No	0	B-
104	Beacon Falls	8.6 µg/L	No	1	A
105	Hampton	5.7 µg/L	No	12	B-
106	Hampton	5.7 µg/L	No	1	B
107	East Windsor	2.6 µg/L	No	6	C+
108	East Lyme	1.9 µg/L	No	6	C
109	East Granby	1.6 µg/L	No	9	F
110	East 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 27.3 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), Beacon Falls (49.0 µg/L), Beacon Falls (49.0 µg/L), Beacon Falls (49.0 µg/L), Beacon Falls (49.0 µg/L). Note: this data is from UCMR 4 testing (2018–2020) and may not reflect current levels.

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