Manganese Contamination

Manganese in Connecticut Drinking Water

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

Cities Tested

Over SMCL

49%

% Over SMCL

604.9 µg/L

State Avg

▲ 31% vs national

vs National

105

Health Violations

Analysis

Manganese in Connecticut: what the data shows

Connecticut has 93 cities with manganese data from the EPA's UCMR 4 program (2018–2020). Manganese exceeded the 50 µg/L EPA secondary MCL in 46 of those cities. The state average max detected level is 604.9 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

49%

46 of 93 cities

→ ▲ 31% above national rate (worse)

National avg

18%

716 of 4016 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	0	B+
2	Bethany	2280.0 µg/L	Over SMCL	4	C-
3	Branford	2280.0 µg/L	Over SMCL	0	A-
4	Cheshire	2280.0 µg/L	Over SMCL	28	F
5	Derby	2280.0 µg/L	Over SMCL	0	B+
6	East Haven	2280.0 µg/L	Over SMCL	0	A-
7	Hamden	2280.0 µg/L	Over SMCL	0	A-
8	Milford	2280.0 µg/L	Over SMCL	0	B+
9	New Haven	2280.0 µg/L	Over SMCL	0	A-
10	North Branford	2280.0 µg/L	Over SMCL	25	F
11	North Haven	2280.0 µg/L	Over SMCL	0	C-
12	Orange	2280.0 µg/L	Over SMCL	0	B+
13	Prospect	2280.0 µg/L	Over SMCL	1	C+
14	Seymour	2280.0 µg/L	Over SMCL	2	D+
15	West Haven	2280.0 µg/L	Over SMCL	0	B+
16	Woodbridge	2280.0 µg/L	Over SMCL	0	B+
17	Meriden	2280.0 µg/L	Over SMCL	4	C+
18	Southington	2280.0 µg/L	Over SMCL	12	F
19	Wallingford	2280.0 µg/L	Over SMCL	4	D
20	Wolcott	2280.0 µg/L	Over SMCL	18	F
21	Farmington	1730.0 µg/L	Over SMCL	3	D+
22	Plainville	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	New Canaan	459.0 µg/L	Over SMCL	7	F
26	Westport	459.0 µg/L	Over SMCL	2	C-
27	Wilton	459.0 µg/L	Over SMCL	7	D
28	Norwalk	459.0 µg/L	Over SMCL	7	D
29	Plymouth	228.0 µg/L	Over SMCL	18	C
30	Groton	170.0 µg/L	Over SMCL	17	F
31	Stonington	170.0 µg/L	Over SMCL	6	B
32	Ledyard	170.0 µg/L	Over SMCL	23	D+
33	Hampton	164.0 µg/L	Over SMCL	1	B
34	Beacon Falls	87.0 µg/L	Over SMCL	3	C-
35	Waterbury	87.0 µg/L	Over SMCL	14	C
36	Naugatuck	87.0 µg/L	Over SMCL	1	A
37	Bridgeport	74.3 µg/L	Over SMCL	2	C-
38	Darien	74.3 µg/L	Over SMCL	7	F
39	Fairfield	74.3 µg/L	Over SMCL	2	C-
40	Redding	74.3 µg/L	Over SMCL	2	C-
41	Shelton	74.3 µg/L	Over SMCL	2	C-
42	Stamford	74.3 µg/L	Over SMCL	4	F
43	Stratford	74.3 µg/L	Over SMCL	2	C-
44	Newtown	74.3 µg/L	Over SMCL	46	F
45	Greenwich	74.3 µg/L	Over SMCL	5	F
46	Oxford	51.2 µg/L	Over SMCL	6	B
47	South Windsor	42.2 µg/L	No	5	C
48	Windsor Locks	42.2 µg/L	No	0	B-
49	East Windsor	42.2 µg/L	No	25	F
50	Ellington	42.2 µg/L	No	0	B
51	Suffield	42.2 µg/L	No	1	C+
52	Manchester	42.2 µg/L	No	8	C
53	Mansfield	42.2 µg/L	No	85	F
54	Enfield	42.2 µg/L	No	9	D
55	Tolland	42.2 µg/L	No	24	F
56	Stafford	42.2 µg/L	No	12	C
57	Clinton	31.6 µg/L	No	4	D+
58	Guilford	31.6 µg/L	No	20	D
59	Madison	31.6 µg/L	No	18	C+
60	Old Saybrook	31.6 µg/L	No	0	B-
61	Westbrook	31.6 µg/L	No	7	C+
62	Glastonbury	24.5 µg/L	No	4	B+
63	Watertown	19.3 µg/L	No	11	D+
64	Danbury	17.1 µg/L	No	59	F
65	Bethel	17.1 µg/L	No	25	F
66	Brookfield	17.1 µg/L	No	135	F
67	Mashantucket	15.7 µg/L	No	7	B
68	East Hartford	14.4 µg/L	No	0	A-
69	Hartford	14.4 µg/L	No	0	A-
70	Newington	14.4 µg/L	No	1	D
71	Rocky Hill	14.4 µg/L	No	1	B
72	West Hartford	14.4 µg/L	No	0	B+
73	Wethersfield	14.4 µg/L	No	0	A-
74	Windsor	14.4 µg/L	No	0	A-
75	Cromwell	14.4 µg/L	No	1	B
76	Berlin	14.4 µg/L	No	6	F
77	Portland	14.4 µg/L	No	9	C
78	Avon	9.6 µg/L	No	3	C+
79	Harwinton	9.4 µg/L	No	5	D
80	Torrington	9.4 µg/L	No	3	B+
81	Granby	7.1 µg/L	No	3	C+
82	Bozrah	6.1 µg/L	No	13	B
83	Franklin	6.1 µg/L	No	13	B
84	Lisbon	6.1 µg/L	No	27	F
85	Montville	6.1 µg/L	No	143	F
86	Norwich	6.1 µg/L	No	19	B-
87	Preston	6.1 µg/L	No	23	D+
88	Uncasville	5.4 µg/L	No	1	A
89	New Britain	3.5 µg/L	No	0	B-
90	Waterford	2.0 µg/L	No	16	C-
91	New London	2.0 µg/L	No	0	C+
92	Middletown	1.1 µg/L	No	11	D
93	Somers	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). 46 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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