Manganese Contamination

Manganese in Connecticut Drinking Water

Ranked by max manganese detected (µg/L) · UCMR 4 data (2018–2020) · Data from EPA SDWIS & UCMR

110

Cities Tested

Over SMCL

48%

% Over SMCL

519.8 µg/L

State Avg

▲ 30% vs national

vs National

134

Health Violations

Analysis

Manganese in Connecticut: what the data shows

Connecticut has 110 cities with manganese data from the EPA's UCMR 4 program (2018–2020). Manganese exceeded the 50 µg/L EPA secondary MCL in 53 of those cities. The state average max detected level is 519.8 µg/L. Manganese occurs naturally in groundwater and surface water. Elevated levels are common in areas with iron-rich geology and in systems that draw from reservoirs with low dissolved oxygen. The secondary MCL of 50 µg/L is based on aesthetic concerns (taste, staining), but health-based guidelines suggest neurological effects at higher concentrations. Emerging research links chronic manganese exposure in drinking water to neurodevelopmental effects in children, including reduced IQ and behavioral issues. Oxidation filtration and water softeners are effective at removing manganese from household water.

Comparison

Cities exceeding 50 µg/L EPA Secondary MCL

Connecticut

48%

53 of 110 cities

→ ▲ 30% above national rate (worse)

National avg

18%

729 of 4068 cities

City Map

Manganese data across Connecticut

Each dot is a city with UCMR 4 manganese testing data. Cities where manganese exceeds the 50 µg/L EPA secondary MCL are highlighted. Size reflects population served.

Worst Offenders

Top 10 cities by manganese level in Connecticut

Highest Manganese levels (µg/L)

All Cities

All Connecticut cities ranked by manganese level

#	City	Level	Over SMCL?	Violations	Grade
1	Ansonia	2280.0 µg/L	Over SMCL	2	D
2	Ansonia	2280.0 µg/L	Over SMCL	12	F
3	Ansonia	2280.0 µg/L	Over SMCL	18	F
4	Ansonia	2280.0 µg/L	Over SMCL	1	C+
5	Ansonia	2280.0 µg/L	Over SMCL	28	F
6	Ansonia	2280.0 µg/L	Over SMCL	4	D
7	Ansonia	2280.0 µg/L	Over SMCL	4	C+
8	Ansonia	2280.0 µg/L	Over SMCL	0	C-
9	Ansonia	2280.0 µg/L	Over SMCL	4	D+
10	Ansonia	2280.0 µg/L	Over SMCL	0	B+
11	Ansonia	2280.0 µg/L	Over SMCL	0	B+
12	Ansonia	2280.0 µg/L	Over SMCL	0	B+
13	Ansonia	2280.0 µg/L	Over SMCL	0	B+
14	Ansonia	2280.0 µg/L	Over SMCL	25	F
15	Ansonia	2280.0 µg/L	Over SMCL	0	B+
16	Ansonia	2280.0 µg/L	Over SMCL	0	B+
17	Ansonia	2280.0 µg/L	Over SMCL	0	B+
18	Ansonia	2280.0 µg/L	Over SMCL	0	B+
19	Ansonia	2280.0 µg/L	Over SMCL	0	B+
20	Ansonia	2280.0 µg/L	Over SMCL	0	B+
21	Berlin	1730.0 µg/L	Over SMCL	3	D+
22	Berlin	1730.0 µg/L	Over SMCL	4	C
23	Bristol	1730.0 µg/L	Over SMCL	4	C+
24	East Lyme	828.0 µg/L	Over SMCL	6	C
25	Beacon Falls	459.0 µg/L	Over SMCL	7	D
26	Beacon Falls	459.0 µg/L	Over SMCL	7	D
27	Beacon Falls	459.0 µg/L	Over SMCL	7	D
28	Beacon Falls	459.0 µg/L	Over SMCL	2	C-
29	Bristol	228.0 µg/L	Over SMCL	18	C
30	Bristol	228.0 µg/L	Over SMCL	9	C
31	Groton	170.0 µg/L	Over SMCL	23	D+
32	Groton	170.0 µg/L	Over SMCL	17	F
33	Groton	170.0 µg/L	Over SMCL	6	B-
34	Hampton	164.0 µg/L	Over SMCL	12	B-
35	Hampton	164.0 µg/L	Over SMCL	1	B
36	Beacon Falls	87.0 µg/L	Over SMCL	3	C-
37	Middlebury	87.0 µg/L	Over SMCL	14	C
38	Beacon Falls	87.0 µg/L	Over SMCL	1	A
39	Beacon Falls	74.3 µg/L	Over SMCL	4	F
40	Beacon Falls	74.3 µg/L	Over SMCL	7	F
41	Beacon Falls	74.3 µg/L	Over SMCL	5	F
42	Beacon Falls	74.3 µg/L	Over SMCL	27	F
43	Beacon Falls	74.3 µg/L	Over SMCL	46	F
44	Beacon Falls	74.3 µg/L	Over SMCL	7	F
45	Beacon Falls	74.3 µg/L	Over SMCL	2	F
46	Beacon Falls	74.3 µg/L	Over SMCL	2	F
47	Beacon Falls	74.3 µg/L	Over SMCL	2	F
48	Beacon Falls	74.3 µg/L	Over SMCL	2	C-
49	Beacon Falls	74.3 µg/L	Over SMCL	2	C-
50	Beacon Falls	74.3 µg/L	Over SMCL	2	C-
51	Beacon Falls	74.3 µg/L	Over SMCL	2	C-
52	Beacon Falls	74.3 µg/L	Over SMCL	2	C-
53	Ansonia	51.2 µg/L	Over SMCL	6	B-
54	Berlin	42.2 µg/L	No	5	C
55	Berlin	42.2 µg/L	No	8	C
56	Berlin	42.2 µg/L	No	40	F
57	Berlin	42.2 µg/L	No	0	B-
58	East Granby	42.2 µg/L	No	5	C-
59	East Granby	42.2 µg/L	No	85	F
60	East Granby	42.2 µg/L	No	9	D
61	East Granby	42.2 µg/L	No	25	F
62	East Granby	42.2 µg/L	No	24	F
63	East Granby	42.2 µg/L	No	12	C-
64	East Granby	42.2 µg/L	No	1	C+
65	East Granby	42.2 µg/L	No	0	B
66	Clinton	31.6 µg/L	No	18	C+
67	Clinton	31.6 µg/L	No	20	D
68	Clinton	31.6 µg/L	No	4	D+
69	Clinton	31.6 µg/L	No	7	C+
70	Clinton	31.6 µg/L	No	0	B-
71	Berlin	24.5 µg/L	No	4	B+
72	Middlebury	19.3 µg/L	No	11	D+
73	Bethel	17.1 µg/L	No	135	F
74	Bethel	17.1 µg/L	No	59	F
75	Bethel	17.1 µg/L	No	25	F
76	Mashantucket	15.7 µg/L	No	7	B
77	Berlin	14.4 µg/L	No	6	F
78	Berlin	14.4 µg/L	No	1	D
79	Berlin	14.4 µg/L	No	0	B+
80	Berlin	14.4 µg/L	No	1	B-
81	Berlin	14.4 µg/L	No	9	C
82	Berlin	14.4 µg/L	No	33	F
83	Berlin	14.4 µg/L	No	1	B
84	Berlin	14.4 µg/L	No	0	A-
85	Berlin	14.4 µg/L	No	0	A-
86	Berlin	14.4 µg/L	No	0	A-
87	Berlin	14.4 µg/L	No	0	A-
88	Middlebury	9.9 µg/L	No	18	C-
89	Plainville	9.6 µg/L	No	3	C+
90	East Granby	9.6 µg/L	No	9	F
91	Windham	9.5 µg/L	No	11	B+
92	Harwinton	9.4 µg/L	No	8	F
93	Harwinton	9.4 µg/L	No	19	F
94	Harwinton	9.4 µg/L	No	3	B+
95	Harwinton	9.4 µg/L	No	5	D
96	East Granby	7.1 µg/L	No	3	C+
97	Franklin	6.1 µg/L	No	143	F
98	Franklin	6.1 µg/L	No	27	F
99	Franklin	6.1 µg/L	No	32	F
100	Franklin	6.1 µg/L	No	19	B-
101	Franklin	6.1 µg/L	No	23	D+
102	Franklin	6.1 µg/L	No	13	B
103	Franklin	6.1 µg/L	No	13	B
104	Uncasville	5.4 µg/L	No	1	A
105	Berlin	3.5 µg/L	No	0	B-
106	New London	2.0 µg/L	No	16	C-
107	New London	2.0 µg/L	No	0	C+
108	Cromwell	1.1 µg/L	No	11	D
109	Cromwell	1.1 µg/L	No	25	F
110	East Windsor	0.4 µg/L	No	6	C+

FAQ

Frequently asked questions about manganese in Connecticut

Is manganese in Connecticut tap water harmful?

The EPA secondary MCL for manganese is 50 µg/L, set primarily for aesthetic reasons (taste, color, staining). 53 cities in Connecticut exceed the secondary MCL. However, emerging research links chronic manganese exposure above 50–100 µg/L to neurodevelopmental effects in children, including reduced IQ.

How can I remove manganese from my drinking water?

Oxidation filtration (such as greensand or birm filters) is the most common and effective method for removing manganese from well water. Water softeners using ion exchange also work well. Standard carbon filters provide limited manganese removal. If your water has a metallic taste or brown/black discoloration, manganese may be the cause.

What causes high manganese in Connecticut water?

Manganese occurs naturally in groundwater and surface water, particularly in areas with iron-rich geology. Low dissolved oxygen conditions (common in deep wells and reservoir bottom waters) increase manganese solubility. Industrial sources include mining, steel production, and battery manufacturing. Seasonal changes in reservoir water chemistry can cause manganese spikes.

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