Arsenic Contamination

Arsenic in Montana Drinking Water

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

Cities Tested

Has Violations

100%

% Has Violations

7.6 violations

State Avg

▼ 0% vs national

vs National

Health Violations

Analysis

Arsenic in Montana: what the data shows

Montana has 92 cities with arsenic-related violations on record. Arsenic contamination is a federal MCL violation at levels above 10 µg/L (10 ppb). The state has 92 cities with at least one arsenic violation. Arsenic enters drinking water primarily through erosion of natural deposits, particularly in western states with arsenite-bearing geology. Industrial sources include mining runoff, glass manufacturing, and semiconductor production. Groundwater systems are significantly more likely to have arsenic issues than surface water systems. Long-term arsenic exposure above the MCL increases the risk of bladder, lung, and skin cancer, as well as cardiovascular disease and diabetes. Reverse osmosis and specialized arsenic-removal media are the most effective point-of-use treatment options.

Comparison

Cities exceeding 10 µg/L EPA MCL

Montana

100%

92 of 92 cities

← = Exactly at national rate

National avg

100%

5489 of 5489 cities

City Map

Arsenic data across Montana

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

Worst Offenders

Top 10 cities by arsenic level in Montana

Highest Arsenic levels (violations)

All Cities

All Montana cities ranked by arsenic level

#	City	Level	Violations?	Violations	Grade
1	Helena	69 violations	Yes	90	F
2	Missoula	60 violations	Yes	189	F
3	Great Falls	49 violations	Yes	64	F
4	Livingston	38 violations	Yes	40	D
5	Dillon	36 violations	Yes	36	F
6	Kalispell	35 violations	Yes	162	F
7	Thompson Falls	23 violations	Yes	27	B+
8	Bozeman	17 violations	Yes	57	F
9	Cut Bank	17 violations	Yes	29	D
10	East Helena	16 violations	Yes	9	D+
11	Manhattan	13 violations	Yes	8	D+
12	Havre	12 violations	Yes	151	F
13	Libby	12 violations	Yes	50	F
14	Lolo	12 violations	Yes	14	D+
15	Billings	11 violations	Yes	51	F
16	Deer Lodge	11 violations	Yes	7	D
17	Shelby	11 violations	Yes	50	D
18	Pablo	10 violations	Yes	116	F
19	Clancy	10 violations	Yes	68	F
20	West Yellowstone	9 violations	Yes	10	D
21	White Sulphur Springs	9 violations	Yes	44	D+
22	Valier	9 violations	Yes	21	B
23	Hamilton	8 violations	Yes	20	D+
24	Lewistown	8 violations	Yes	99	D
25	Conrad	8 violations	Yes	29	D
26	Anaconda	7 violations	Yes	12	D+
27	Harlem	7 violations	Yes	237	D
28	Pinesdale	7 violations	Yes	17	B
29	Whitefish	6 violations	Yes	42	F
30	Harlowton	6 violations	Yes	9	C+
31	Frenchtown	6 violations	Yes	28	C+
32	Corwin Springs	6 violations	Yes	18	C+
33	Glendive	5 violations	Yes	16	D
34	Sidney	5 violations	Yes	27	F
35	Joliet	5 violations	Yes	0	A-
36	Stanford	5 violations	Yes	3	C-
37	Hardin	4 violations	Yes	6	F
38	Lame Deer	4 violations	Yes	54	F
39	Forsyth	4 violations	Yes	5	A-
40	Townsend	4 violations	Yes	3	B
41	Crow Agency	4 violations	Yes	43	D
42	Three Forks	4 violations	Yes	2	A
43	Malta	4 violations	Yes	0	D
44	Chester	4 violations	Yes	26	D
45	Seeley Lake	4 violations	Yes	6	B+
46	Absarokee	4 violations	Yes	4	B+
47	Sand Coulee	4 violations	Yes	10	C-
48	Laurel	3 violations	Yes	6	C+
49	Polson	3 violations	Yes	26	D+
50	Columbia Falls	3 violations	Yes	23	D
51	Ronan	3 violations	Yes	14	C-
52	Colstrip	3 violations	Yes	2	A-
53	Red Lodge	3 violations	Yes	4	B
54	Choteau	3 violations	Yes	5	B-
55	Whitehall	3 violations	Yes	64	D+
56	Ashland	3 violations	Yes	49	D+
57	Gardiner	3 violations	Yes	0	A
58	Belgrade	2 violations	Yes	27	F
59	Browning	2 violations	Yes	40	F
60	Box Elder	2 violations	Yes	21	B-
61	Eureka	2 violations	Yes	16	C-
62	Stevensville	2 violations	Yes	13	B-
63	Lakeside	2 violations	Yes	20	B+
64	Columbus	2 violations	Yes	8	D
65	Plains	2 violations	Yes	0	B+
66	Philipsburg	2 violations	Yes	19	F
67	Fairfield	2 violations	Yes	0	B-
68	Darby	2 violations	Yes	26	C
69	Fort Peck	2 violations	Yes	9	B-
70	Bridger	2 violations	Yes	0	A-
71	Alberton	2 violations	Yes	2	A-
72	Wibaux	2 violations	Yes	9	D+
73	Butte	1 violations	Yes	4	B+
74	Bigfork	1 violations	Yes	20	A-
75	Culbertson	1 violations	Yes	6	B+
76	Troy	1 violations	Yes	6	B+
77	Black Eagle	1 violations	Yes	11	B
78	Big Timber	1 violations	Yes	6	B+
79	Fort Benton	1 violations	Yes	1	B+
80	Virginia City	1 violations	Yes	11	C+
81	Chinook	1 violations	Yes	15	B
82	Somers	1 violations	Yes	4	A-
83	Ballantine	1 violations	Yes	8	C+
84	Ballantine	1 violations	Yes	8	C+
85	Sunburst	1 violations	Yes	5	B
86	Belt	1 violations	Yes	10	B+
87	Warm Springs	1 violations	Yes	0	B
88	Huntley	1 violations	Yes	2	B+
89	Sheridan	1 violations	Yes	0	C-
90	Sun River	1 violations	Yes	2	A-
91	Santa Rita	1 violations	Yes	0	A-
92	Hot Springs	1 violations	Yes	1	A-

FAQ

Frequently asked questions about arsenic in Montana

Is arsenic in Montana tap water a concern?

Yes — 92 cities in Montana have arsenic-related violations on record. The EPA MCL for arsenic is 10 µg/L. Even at levels below the MCL, long-term arsenic exposure has been linked to cancer and cardiovascular disease.

How can I remove arsenic from my drinking water in Montana?

Reverse osmosis (RO) systems are the most effective at removing arsenic, typically reducing it by 90% or more. Specialized arsenic-removal media (such as iron-based adsorption filters) are also highly effective. Standard carbon filters and pitcher filters do NOT effectively remove arsenic. If your water comes from a private well, have it tested for arsenic.

Where does arsenic in Montana water come from?

Arsenic enters drinking water primarily through natural erosion of arsenic-bearing rock formations. It is most common in groundwater systems in the western United States, parts of the Midwest, and New England. Industrial sources include mining, smelting, and agricultural pesticide residues. Groundwater sources are far more likely to contain arsenic than surface water.

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