Nitrate Contamination

Nitrate in Connecticut Drinking Water

Ranked by nitrate violation count · Data from EPA SDWIS & UCMR

117

Cities Tested

117

Has Violations

100%

% Has Violations

8.7 violations

State Avg

▼ 0% vs national

vs National

134

Health Violations

Analysis

Nitrate in Connecticut: what the data shows

Connecticut has 117 cities with nitrate-related violations. The EPA MCL for nitrate is 10 mg/L (measured as nitrogen). The state has 117 cities with at least one nitrate violation. Nitrate is the most common groundwater contaminant in the United States. It enters water supplies primarily through agricultural fertilizer runoff, septic system leaching, and animal feedlot operations. Rural and agricultural communities face the highest risk. The primary acute health concern is methemoglobinemia ("blue baby syndrome") in infants under six months. Emerging research also links chronic nitrate exposure to thyroid disease, certain cancers, and adverse birth outcomes. Reverse osmosis, ion exchange, and distillation can remove nitrate from drinking water — standard carbon filters do not.

Comparison

Cities exceeding 10 mg/L EPA MCL

Connecticut

100%

117 of 117 cities

← = Exactly at national rate

National avg

100%

8001 of 8001 cities

City Map

Nitrate data across Connecticut

Each dot is a city with nitrate violation data. Cities with at least one nitrate-related violation are highlighted. Size reflects population served.

Worst Offenders

Top 10 cities by nitrate level in Connecticut

Highest Nitrate levels (violations)

All Cities

All Connecticut cities ranked by nitrate level

#	City	Level	Violations?	Violations	Grade
1	Ansonia	35 violations	Yes	28	F
2	Ansonia	32 violations	Yes	12	F
3	Bethel	30 violations	Yes	135	F
4	Bethel	30 violations	Yes	59	F
5	East Granby	28 violations	Yes	85	F
6	Brookfield	27 violations	Yes	56	D+
7	East Granby	23 violations	Yes	25	F
8	Groton	23 violations	Yes	17	F
9	Berlin	21 violations	Yes	6	F
10	Berlin	21 violations	Yes	40	F
11	East Granby	21 violations	Yes	12	C-
12	Ansonia	20 violations	Yes	4	D
13	Ansonia	20 violations	Yes	4	C+
14	East Granby	20 violations	Yes	9	D
15	East Granby	20 violations	Yes	1	C+
16	Berlin	18 violations	Yes	5	C
17	Berlin	18 violations	Yes	8	C
18	Berlin	18 violations	Yes	0	B-
19	East Granby	18 violations	Yes	5	C-
20	East Granby	18 violations	Yes	24	F
21	East Granby	18 violations	Yes	0	B
22	Bethel	17 violations	Yes	25	F
23	Colchester	17 violations	Yes	34	D
24	East Hampton	17 violations	Yes	64	D
25	Franklin	14 violations	Yes	143	F
26	Clinton	14 violations	Yes	4	D+
27	Ansonia	13 violations	Yes	18	F
28	Clinton	13 violations	Yes	18	C+
29	Clinton	13 violations	Yes	20	D
30	Clinton	13 violations	Yes	7	C+
31	Clinton	13 violations	Yes	0	B-
32	Ansonia	12 violations	Yes	25	F
33	Beacon Falls	11 violations	Yes	27	F
34	Bristol	11 violations	Yes	18	C
35	Woodbury	11 violations	Yes	18	D+
36	Durham	11 violations	Yes	46	D
37	Beacon Falls	10 violations	Yes	2	F
38	Harwinton	10 violations	Yes	19	F
39	Coventry	10 violations	Yes	34	F
40	Old Lyme	9 violations	Yes	42	D
41	Ashford	9 violations	Yes	32	D
42	Killingly	8 violations	Yes	32	F
43	Beacon Falls	7 violations	Yes	46	F
44	Bristol	7 violations	Yes	9	C
45	Chester	7 violations	Yes	10	D
46	Chester	7 violations	Yes	5	C
47	Willington	7 violations	Yes	41	F
48	Lewisboro (T)	7 violations	Yes	3	B+
49	Harwinton	6 violations	Yes	8	F
50	Putnam	6 violations	Yes	120	F
51	Chester	6 violations	Yes	12	B-
52	Kent	6 violations	Yes	30	D
53	East Haddam	6 violations	Yes	26	D
54	Lower Sipaulovi, Lower Mishongnovi	6 violations	Yes	63	D
55	Lower Sipaulovi, Lower Mishongnovi	6 violations	Yes	63	D
56	Berlin	5 violations	Yes	1	D
57	Ansonia	5 violations	Yes	4	D+
58	Groton	5 violations	Yes	23	D+
59	Franklin	5 violations	Yes	27	F
60	Hebron	5 violations	Yes	21	F
61	Ansonia	4 violations	Yes	2	D
62	Ansonia	4 violations	Yes	1	C+
63	Ansonia	4 violations	Yes	0	C-
64	Ansonia	4 violations	Yes	0	B+
65	Ansonia	4 violations	Yes	0	B+
66	Ansonia	4 violations	Yes	0	B+
67	Ansonia	4 violations	Yes	0	B+
68	Ansonia	4 violations	Yes	0	B+
69	Ansonia	4 violations	Yes	0	B+
70	Ansonia	4 violations	Yes	0	B+
71	Ansonia	4 violations	Yes	0	B+
72	Ansonia	4 violations	Yes	0	B+
73	Ansonia	4 violations	Yes	0	B+
74	Berlin	4 violations	Yes	33	F
75	Cromwell	4 violations	Yes	25	F
76	Harwinton	4 violations	Yes	5	D
77	Hampton	4 violations	Yes	12	B-
78	Groton	4 violations	Yes	6	B-
79	Middlebury	4 violations	Yes	15	F
80	Barkhamsted	4 violations	Yes	12	C
81	Avon	4 violations	Yes	8	C
82	Plainfield	4 violations	Yes	37	D
83	Salisbury	4 violations	Yes	4	B+
84	Marlborough	4 violations	Yes	19	D
85	Sprague	4 violations	Yes	0	B+
86	Sharon	4 violations	Yes	9	F
87	Killingworth	4 violations	Yes	35	C-
88	Berlin	3 violations	Yes	4	C
89	Cromwell	3 violations	Yes	11	D
90	Franklin	3 violations	Yes	32	F
91	Killingly	3 violations	Yes	14	C-
92	Griswold	3 violations	Yes	53	F
93	North Stonington	3 violations	Yes	19	C
94	Washington	3 violations	Yes	31	F
95	Hopkinton	3 violations	Yes	37	F
96	Berlin	2 violations	Yes	3	D+
97	Berlin	2 violations	Yes	0	B+
98	Beacon Falls	2 violations	Yes	7	F
99	Beacon Falls	2 violations	Yes	2	F
100	Middlebury	2 violations	Yes	11	D+
101	Berlin	2 violations	Yes	0	B-
102	New London	2 violations	Yes	16	C-
103	New London	2 violations	Yes	0	C+
104	Harwinton	2 violations	Yes	3	B+
105	Franklin	2 violations	Yes	19	B-
106	East Granby	2 violations	Yes	9	F
107	East Windsor	2 violations	Yes	6	C+
108	Plymouth	2 violations	Yes	0	A+
109	Carroll	2 violations	Yes	10	C
110	Carroll	2 violations	Yes	9	C
111	Beacon Falls	1 violations	Yes	4	F
112	Beacon Falls	1 violations	Yes	5	F
113	Beacon Falls	1 violations	Yes	2	F
114	Bristol	1 violations	Yes	4	C+
115	Hampton	1 violations	Yes	1	B
116	East Granby	1 violations	Yes	3	C+
117	Bow	1 violations	Yes	53	D

FAQ

Frequently asked questions about nitrate in Connecticut

Is nitrate in Connecticut tap water dangerous?

Yes — 117 cities in Connecticut have nitrate-related violations. The EPA MCL is 10 mg/L. Nitrate is especially dangerous for infants under six months, where it can cause methemoglobinemia ("blue baby syndrome"). Adults face lower acute risk, but chronic exposure is linked to thyroid disease and certain cancers.

How can I remove nitrate from my drinking water?

Reverse osmosis, ion exchange, and distillation are effective at removing nitrate. Standard carbon filters (including most pitcher and faucet-mount filters) do NOT remove nitrate. If you rely on a private well in an agricultural area, have your water tested annually for nitrate.

What causes high nitrate levels in Connecticut water?

Nitrate contamination comes primarily from agricultural fertilizer runoff, septic system leaching, and animal feedlot operations. Rural communities near intensive farming are most at risk. Shallow wells are particularly vulnerable. Heavy rainfall can spike nitrate levels as it washes fertilizer into groundwater and surface water supplies.

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