Nitrate Contamination

Nitrate in Connecticut Drinking Water

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

Cities Tested

Has Violations

100%

% Has Violations

9.2 violations

State Avg

▼ 0% vs national

vs National

105

Health Violations

Analysis

Nitrate in Connecticut: what the data shows

Connecticut has 93 cities with nitrate-related violations. The EPA MCL for nitrate is 10 mg/L (measured as nitrogen). The state has 93 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%

93 of 93 cities

← = Exactly at national rate

National avg

100%

7727 of 7727 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	Cheshire	35 violations	Yes	28	F
2	Southington	32 violations	Yes	12	F
3	Danbury	30 violations	Yes	59	F
4	Brookfield	30 violations	Yes	135	F
5	Mansfield	28 violations	Yes	85	F
6	New Fairfield	27 violations	Yes	56	D+
7	East Windsor	23 violations	Yes	25	F
8	Groton	23 violations	Yes	17	F
9	Berlin	21 violations	Yes	6	F
10	Stafford	21 violations	Yes	12	C
11	Suffield	20 violations	Yes	1	C+
12	Meriden	20 violations	Yes	4	C+
13	Wallingford	20 violations	Yes	4	D
14	Enfield	20 violations	Yes	9	D
15	South Windsor	18 violations	Yes	5	C
16	Windsor Locks	18 violations	Yes	0	B-
17	Ellington	18 violations	Yes	0	B
18	Manchester	18 violations	Yes	8	C
19	Tolland	18 violations	Yes	24	F
20	Bethel	17 violations	Yes	25	F
21	Colchester	17 violations	Yes	34	D
22	East Hampton	17 violations	Yes	64	D
23	Montville	14 violations	Yes	143	F
24	Clinton	14 violations	Yes	4	D+
25	Guilford	13 violations	Yes	20	D
26	Madison	13 violations	Yes	18	C+
27	Old Saybrook	13 violations	Yes	0	B-
28	Westbrook	13 violations	Yes	7	C+
29	Wolcott	13 violations	Yes	18	F
30	North Branford	12 violations	Yes	25	F
31	Plymouth	11 violations	Yes	18	C
32	Durham	11 violations	Yes	46	D
33	Woodbury	11 violations	Yes	18	D+
34	Old Lyme	9 violations	Yes	42	D
35	Killingly	8 violations	Yes	32	F
36	Deep River	7 violations	Yes	5	C
37	Newtown	7 violations	Yes	46	F
38	Willington	7 violations	Yes	41	F
39	Lewisboro (T)	7 violations	Yes	3	B+
40	Kent	6 violations	Yes	30	D
41	Woodstock	6 violations	Yes	120	F
42	Lower Sipaulovi, Lower Mishongnovi	6 violations	Yes	63	D
43	Lower Sipaulovi, Lower Mishongnovi	6 violations	Yes	63	D
44	Bethany	5 violations	Yes	4	C-
45	Newington	5 violations	Yes	1	D
46	Lisbon	5 violations	Yes	27	F
47	Ledyard	5 violations	Yes	23	D+
48	Hebron	5 violations	Yes	21	F
49	Ansonia	4 violations	Yes	0	B+
50	Branford	4 violations	Yes	0	A-
51	Derby	4 violations	Yes	0	B+
52	East Haven	4 violations	Yes	0	A-
53	Hamden	4 violations	Yes	0	A-
54	Milford	4 violations	Yes	0	B+
55	New Haven	4 violations	Yes	0	A-
56	North Haven	4 violations	Yes	0	C-
57	Orange	4 violations	Yes	0	B+
58	Prospect	4 violations	Yes	1	C+
59	Seymour	4 violations	Yes	2	D+
60	West Haven	4 violations	Yes	0	B+
61	Woodbridge	4 violations	Yes	0	B+
62	Harwinton	4 violations	Yes	5	D
63	Stonington	4 violations	Yes	6	B
64	Barkhamsted	4 violations	Yes	12	C
65	Plainfield	4 violations	Yes	37	D
66	Sprague	4 violations	Yes	0	B+
67	Sharon	4 violations	Yes	9	F
68	Southbury	4 violations	Yes	15	D
69	Killingworth	4 violations	Yes	35	C-
70	Salisbury	4 violations	Yes	4	A-
71	Plainville	3 violations	Yes	4	C
72	Middletown	3 violations	Yes	11	D
73	Griswold	3 violations	Yes	53	F
74	Brooklyn	3 violations	Yes	14	C-
75	North Stonington	3 violations	Yes	19	C
76	Washington	3 violations	Yes	31	F
77	Farmington	2 violations	Yes	3	D+
78	West Hartford	2 violations	Yes	0	B+
79	New Britain	2 violations	Yes	0	B-
80	Waterford	2 violations	Yes	16	C-
81	Torrington	2 violations	Yes	3	B+
82	Norwich	2 violations	Yes	19	B-
83	New London	2 violations	Yes	0	C+
84	Somers	2 violations	Yes	6	C+
85	Watertown	2 violations	Yes	11	D+
86	Thomaston	2 violations	Yes	0	A+
87	Carroll	2 violations	Yes	9	C
88	Carroll	2 violations	Yes	10	C
89	Stamford	1 violations	Yes	4	F
90	Bristol	1 violations	Yes	4	C+
91	Hampton	1 violations	Yes	1	B
92	Granby	1 violations	Yes	3	C+
93	Greenwich	1 violations	Yes	5	F

FAQ

Frequently asked questions about nitrate in Connecticut

Is nitrate in Connecticut tap water dangerous?

Yes — 93 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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