Chromium-6 Contamination

Chromium-6 in Oklahoma Drinking Water

Ranked by max chromium-6 detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR

Cities Tested

Detected

100%

% Detected

6.07 µg/L

State Avg

▼ 0% vs national

vs National

351

Health Violations

Analysis

Chromium-6 in Oklahoma: what the data shows

Oklahoma has 55 cities with chromium-6 data from the EPA's UCMR 3 program (2013–2015). Hexavalent chromium (Cr VI) was detected in 55 of those cities. There is currently no federal MCL for chromium-6 — California's 10 µg/L limit is used as a reference. The state average max detected level is 6.07 µg/L. Chromium-6 occurs naturally in some groundwater aquifers but also from industrial discharge, particularly from steel processing, chrome plating, and leather tanning. It is distinct from trivalent chromium (Cr III), which is an essential nutrient at low doses. The National Toxicology Program and IARC classify chromium-6 as a carcinogen via inhalation; the evidence for drinking water carcinogenicity is strong but regulatory action at the federal level remains pending as of 2026. Reverse osmosis systems effectively remove chromium-6 to near-undetectable levels.

Comparison

Cities exceeding No federal MCL (CA: 10 µg/L)

Oklahoma

100%

55 of 55 cities

← = Exactly at national rate

National avg

100%

4005 of 4005 cities

City Map

Chromium-6 data across Oklahoma

Each dot is a city with UCMR 3 chromium-6 data. Detected cities are shown; there is no federal MCL — California's 10 µg/L limit is used as a reference. Size reflects population served.

Worst Offenders

Top 10 cities by chromium-6 level in Oklahoma

Highest Chromium-6 levels (µg/L)

All Cities

All Oklahoma cities ranked by chromium-6 level

#	City	Level	Detected?	Violations	Grade
1	Norman	97.38 µg/L	Detected	52	F
2	Moore	54.00 µg/L	Detected	53	F
3	Edmond	50.90 µg/L	Detected	86	F
4	Mustang	29.90 µg/L	Detected	9	C+
5	Oklahoma City	23.80 µg/L	Detected	56	F
6	Midwest City	16.40 µg/L	Detected	11	B+
7	Purcell	12.10 µg/L	Detected	1	A-
8	Del City	10.50 µg/L	Detected	12	F
9	Yukon	9.92 µg/L	Detected	18	D
10	Guthrie	5.60 µg/L	Detected	45	F
11	Bethany	4.09 µg/L	Detected	14	B+
12	Woodward	3.18 µg/L	Detected	55	D
13	Thomas	2.80 µg/L	Detected	0	A+
14	Enid	1.58 µg/L	Detected	33	F
15	Elk City	1.47 µg/L	Detected	5	D
16	Sand Springs	1.43 µg/L	Detected	20	B
17	Guymon	1.40 µg/L	Detected	10	A-
18	El Reno	1.31 µg/L	Detected	49	D
19	Blackwell	0.61 µg/L	Detected	65	D+
20	Broken Arrow	0.58 µg/L	Detected	113	F
21	Duncan	0.46 µg/L	Detected	150	D+
22	Mannsville	0.41 µg/L	Detected	4	A-
23	Stillwater	0.36 µg/L	Detected	72	F
24	Muskogee	0.28 µg/L	Detected	246	D
25	Ponca City	0.28 µg/L	Detected	23	F
26	Jenks	0.28 µg/L	Detected	31	B-
27	Oilton	0.26 µg/L	Detected	4	D+
28	Miami	0.21 µg/L	Detected	11	D
29	Ardmore	0.17 µg/L	Detected	188	F
30	Wister	0.16 µg/L	Detected	84	D
31	Stringtown	0.15 µg/L	Detected	144	D+
32	Ada	0.12 µg/L	Detected	6	B-
33	Altus	0.12 µg/L	Detected	162	D
34	Poteau	0.12 µg/L	Detected	56	D
35	Okmulgee	0.11 µg/L	Detected	262	D
36	Tahlequah	0.11 µg/L	Detected	56	F
37	Claremore	0.11 µg/L	Detected	153	F
38	Sapulpa	0.10 µg/L	Detected	85	D
39	Wagoner	0.10 µg/L	Detected	141	F
40	Shawnee	0.09 µg/L	Detected	124	D
41	Bartlesville	0.07 µg/L	Detected	217	F
42	Afton	0.07 µg/L	Detected	89	F
43	Lawton	0.06 µg/L	Detected	23	F
44	Grove	0.06 µg/L	Detected	20	D
45	Tulsa	0.06 µg/L	Detected	6	D
46	Fort Sill	0.05 µg/L	Detected	4	A
47	Bixby	0.05 µg/L	Detected	1	B
48	Sallisaw	0.05 µg/L	Detected	29	D+
49	Mcalester	0.04 µg/L	Detected	670	F
50	Hartshorne	0.04 µg/L	Detected	103	D+
51	Chickasha	0.04 µg/L	Detected	79	F
52	Owasso	0.04 µg/L	Detected	8	C+
53	Collinsville	0.04 µg/L	Detected	24	C+
54	Henryetta	0.04 µg/L	Detected	116	F
55	Durant	0.03 µg/L	Detected	104	D

FAQ

Frequently asked questions about chromium-6 in Oklahoma

Is chromium-6 in Oklahoma tap water dangerous?

Chromium-6 (hexavalent chromium) is a potential human carcinogen. There is currently no federal MCL — California's 10 µg/L limit is the most protective US standard. 55 cities in Oklahoma had detectable chromium-6 in UCMR 3 testing (2013–2015). Reverse osmosis is the most effective removal method.

Where does chromium-6 come from in Oklahoma water?

Chromium-6 enters water supplies from two main sources: natural weathering of chromium-containing rock formations (especially in the Southwest and parts of the Midwest) and industrial discharge from steel mills, chrome plating, and coal ash sites. Groundwater systems are more commonly affected by natural sources, while surface water systems near industrial areas face pollution-related risks.

How can I filter chromium-6 from my water in Oklahoma?

Reverse osmosis (RO) systems are the most effective, removing over 95% of chromium-6. Some high-quality activated alumina or anion exchange filters also provide significant reduction. Standard carbon filters and pitcher filters are generally NOT effective against chromium-6. Look for filters certified by NSF International against NSF/ANSI 58 (for RO systems).

More contaminants