Chlorate Contamination

Chlorate in Massachusetts Drinking Water

Ranked by max chlorate detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR

149

Cities Tested

Over HA

54%

% Over HA

399.0 µg/L

State Avg

▼ 5% vs national

vs National

263

Health Violations

Analysis

Chlorate in Massachusetts: what the data shows

Massachusetts has 149 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 81 of those cities. The state average max detected level is 399.0 µg/L. Chlorate is a disinfection byproduct that forms when chlorine dioxide or hypochlorite solutions are used to disinfect drinking water. It is most common in systems that use chlorine dioxide for taste-and-odor control or that store hypochlorite for extended periods. There is no federal MCL — the EPA lifetime health advisory is 210 µg/L. Chlorate can interfere with thyroid function by blocking iodide uptake, an effect of particular concern for pregnant women, infants, and people with thyroid conditions. Reverse osmosis and ion exchange (anion-specific) are effective at removing chlorate; standard activated carbon filters provide only modest reduction.

Comparison

Cities exceeding 210 µg/L EPA lifetime HA (no MCL)

Massachusetts

54%

81 of 149 cities

← ▼ 5% below national rate (better)

National avg

59%

1866 of 3166 cities

City Map

Chlorate data across Massachusetts

Each dot is a city with UCMR 3 chlorate testing data. Cities where chlorate exceeds the 210 µg/L EPA lifetime health advisory are highlighted. Size reflects population served.

Worst Offenders

Top 10 cities by chlorate level in Massachusetts

Highest Chlorate levels (µg/L)

All Cities

All Massachusetts cities ranked by chlorate level

#	City	Level	Over HA?	Violations	Grade
1	Danvers	11000.0 µg/L	Over HA	5	B+
2	Mansfield	2200.0 µg/L	Over HA	6	A-
3	Maynard	1830.0 µg/L	Over HA	8	B-
4	Westborough	1800.0 µg/L	Over HA	13	D
5	Gloucester	1640.5 µg/L	Over HA	4	A
6	North Reading	1300.0 µg/L	Over HA	9	A-
7	Tewksbury	1100.0 µg/L	Over HA	3	B
8	Foxborough	1000.0 µg/L	Over HA	11	A-
9	East Bridgewater	870.0 µg/L	Over HA	6	B+
10	Swansea	848.0 µg/L	Over HA	12	B+
11	Gardner	779.8 µg/L	Over HA	7	A-
12	Ipswich	740.0 µg/L	Over HA	8	B
13	Taunton	730.0 µg/L	Over HA	1	B+
14	Lawrence	670.0 µg/L	Over HA	3	B+
15	Middleborough	650.0 µg/L	Over HA	16	B
16	Leominster	620.0 µg/L	Over HA	12	B
17	Peabody	614.0 µg/L	Over HA	7	B
18	Bourne	599.3 µg/L	Over HA	16	B-
19	Holliston	593.0 µg/L	Over HA	11	C-
20	Bridgewater	590.0 µg/L	Over HA	5	C+
21	Bellingham	560.0 µg/L	Over HA	21	B-
22	Rowley	550.0 µg/L	Over HA	10	B
23	Billerica	520.0 µg/L	Over HA	7	B+
24	Dighton	500.0 µg/L	Over HA	7	D+
25	Plainville	483.1 µg/L	Over HA	9	B
26	Hudson	480.0 µg/L	Over HA	7	F
27	Beverly	470.0 µg/L	Over HA	0	A-
28	North Adams	470.0 µg/L	Over HA	5	B
29	Southbridge	462.6 µg/L	Over HA	3	A
30	Hanover	460.0 µg/L	Over HA	12	C-
31	Clinton	430.0 µg/L	Over HA	17	A-
32	Milford	421.6 µg/L	Over HA	15	F
33	Brockton	420.0 µg/L	Over HA	5	A-
34	Norwell	420.0 µg/L	Over HA	5	B+
35	Salem	400.0 µg/L	Over HA	0	A-
36	Sudbury	400.0 µg/L	Over HA	10	B-
37	Medway	400.0 µg/L	Over HA	14	B-
38	Wakefield	394.0 µg/L	Over HA	10	B+
39	Attleboro	390.8 µg/L	Over HA	3	A-
40	Methuen	380.0 µg/L	Over HA	1	A
41	Natick	380.0 µg/L	Over HA	3	B+
42	Dracut	370.0 µg/L	Over HA	5	B
43	Newburyport	370.0 µg/L	Over HA	3	A-
44	Chelmsford	360.0 µg/L	Over HA	1	B-
45	Burlington	350.0 µg/L	Over HA	7	B+
46	Walpole	350.0 µg/L	Over HA	6	A-
47	Lowell	342.0 µg/L	Over HA	5	B+
48	Dartmouth	340.0 µg/L	Over HA	16	C+
49	Falmouth	330.0 µg/L	Over HA	23	B
50	Winchester	330.0 µg/L	Over HA	5	C-
51	Norton	310.0 µg/L	Over HA	10	B+
52	Reading	307.0 µg/L	Over HA	1	A-
53	Stoneham	301.0 µg/L	Over HA	15	A-
54	Cambridge	300.0 µg/L	Over HA	2	B+
55	Oak Bluffs	300.0 µg/L	Over HA	18	B+
56	Winthrop	299.0 µg/L	Over HA	8	B+
57	Webster	290.0 µg/L	Over HA	19	B
58	Marblehead	289.0 µg/L	Over HA	7	A-
59	Chelsea	286.0 µg/L	Over HA	17	A-
60	Saugus	286.0 µg/L	Over HA	10	A-
61	New Bedford	280.0 µg/L	Over HA	2	A-
62	Revere	273.0 µg/L	Over HA	13	B+
63	Duxbury	270.0 µg/L	Over HA	4	B+
64	Northampton	263.0 µg/L	Over HA	5	A-
65	Malden	262.0 µg/L	Over HA	20	B-
66	Haverhill	260.0 µg/L	Over HA	1	C
67	Bedford	257.0 µg/L	Over HA	35	B+
68	Melrose	251.0 µg/L	Over HA	16	B
69	Swampscott	240.0 µg/L	Over HA	9	A-
70	Hingham	230.0 µg/L	Over HA	2	C+
71	Andover	230.0 µg/L	Over HA	2	B+
72	Wilmington	227.0 µg/L	Over HA	5	A-
73	South Hadley	224.0 µg/L	Over HA	16	A-
74	Everett	222.0 µg/L	Over HA	8	B+
75	Watertown	221.0 µg/L	Over HA	5	A-
76	Boston	220.0 µg/L	Over HA	5	B
77	Concord	220.0 µg/L	Over HA	4	B+
78	Seekonk	220.0 µg/L	Over HA	7	A-
79	Wayland	220.0 µg/L	Over HA	11	B+
80	Weston	216.0 µg/L	Over HA	16	A-
81	Waltham	214.0 µg/L	Over HA	11	A-
82	Somerville	210.0 µg/L	No	12	B+
83	Whitman	210.0 µg/L	No	5	A-
84	Woburn	209.0 µg/L	No	5	B+
85	Plymouth	200.0 µg/L	No	20	F
86	Arlington	194.0 µg/L	No	4	A-
87	Westfield	193.0 µg/L	No	7	B+
88	Belmont	192.0 µg/L	No	5	B+
89	Medford	191.0 µg/L	No	9	C
90	Barnstable	190.0 µg/L	No	34	D+
91	Salisbury	190.0 µg/L	No	0	A-
92	Scituate	190.0 µg/L	No	10	C
93	Holden	190.0 µg/L	No	18	B
94	Amesbury	190.0 µg/L	No	0	A
95	Brookline	187.0 µg/L	No	6	A-
96	Needham	187.0 µg/L	No	4	A-
97	Milton	185.0 µg/L	No	6	B+
98	Lexington	184.0 µg/L	No	7	B+
99	Norwood	181.0 µg/L	No	8	A-
100	Lynn	180.0 µg/L	No	5	A-
101	Harwich	180.0 µg/L	No	3	A+
102	Stoughton	180.0 µg/L	No	13	B
103	Newton	179.0 µg/L	No	8	B
104	Quincy	175.0 µg/L	No	6	A-
105	Canton	171.0 µg/L	No	11	A-
106	Dennis	170.0 µg/L	No	5	A
107	Franklin	170.0 µg/L	No	11	B+
108	Acton	170.0 µg/L	No	28	F
109	Framingham	168.0 µg/L	No	4	A-
110	Northborough	162.0 µg/L	No	10	B
111	Sandwich	160.0 µg/L	No	13	A
112	Kingston	160.0 µg/L	No	12	C
113	Wellesley	158.0 µg/L	No	20	B
114	Marlborough	150.0 µg/L	No	5	A-
115	Brewster	150.0 µg/L	No	1	B+
116	Provincetown	150.0 µg/L	No	5	A
117	North Attleborough	140.0 µg/L	No	15	F
118	Abington	130.0 µg/L	No	14	B
119	North Andover	130.0 µg/L	No	5	A
120	Wareham	130.0 µg/L	No	22	B
121	Easton	130.0 µg/L	No	3	A-
122	Topsfield	127.3 µg/L	No	8	B+
123	Whately	120.0 µg/L	No	0	B+
124	Chatham	111.0 µg/L	No	19	A
125	Orleans	110.0 µg/L	No	3	B
126	Medfield	110.0 µg/L	No	14	B+
127	Leicester	110.0 µg/L	No	121	D
128	Mattapoisett	100.0 µg/L	No	9	A
129	Sharon	100.0 µg/L	No	5	D+
130	Westford	72.1 µg/L	No	9	B
131	Somerset	67.0 µg/L	No	11	B
132	Pembroke	63.0 µg/L	No	16	A
133	Amherst	61.0 µg/L	No	6	A-
134	Fairhaven	59.0 µg/L	No	9	A
135	Chicopee	57.5 µg/L	No	0	A-
136	Uxbridge	54.0 µg/L	No	2	A-
137	East Longmeadow	53.8 µg/L	No	5	A-
138	Greenfield	49.0 µg/L	No	3	A-
139	Hadley	48.0 µg/L	No	7	A
140	Weymouth	46.0 µg/L	No	6	A
141	Tisbury	44.0 µg/L	No	9	B+
142	Fall River	36.0 µg/L	No	11	B-
143	Easthampton	32.2 µg/L	No	8	A
144	Dedham	30.0 µg/L	No	1	B+
145	Grafton	29.0 µg/L	No	25	F
146	West Springfield	26.0 µg/L	No	7	A
147	Agawam	25.0 µg/L	No	8	A-
148	Marshfield	24.0 µg/L	No	9	B-
149	Longmeadow	23.0 µg/L	No	18	B

FAQ

Frequently asked questions about chlorate in Massachusetts

Is chlorate in Massachusetts tap water dangerous?

Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 81 cities in Massachusetts exceed this level. Chlorate can interfere with thyroid iodide uptake, which is a particular concern for infants, pregnant women, and people with hypothyroidism.

Where does chlorate in Massachusetts water come from?

Chlorate is a byproduct of chlorine-based disinfectants — particularly chlorine dioxide and hypochlorite (bleach) solutions. Levels tend to be higher in systems that use chlorine dioxide for taste-and-odor treatment or store sodium hypochlorite at high concentrations or for long periods. Levels vary seasonally with disinfectant use.

How can I reduce chlorate exposure?

Reverse osmosis is the most effective home treatment for chlorate, typically removing 80–95%. Anion exchange systems also work but require regeneration. Standard activated carbon filters provide only limited chlorate reduction. Boiling does NOT remove chlorate.

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