Chromium-6 Contamination

Chromium-6 in Colorado 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

0.22 µg/L

State Avg

▼ 0% vs national

vs National

206

Health Violations

Analysis

Chromium-6 in Colorado: what the data shows

Colorado has 62 cities with chromium-6 data from the EPA's UCMR 3 program (2013–2015). Hexavalent chromium (Cr VI) was detected in 62 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 0.22 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)

Colorado

100%

62 of 62 cities

← = Exactly at national rate

National avg

100%

4005 of 4005 cities

City Map

Chromium-6 data across Colorado

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 Colorado

Highest Chromium-6 levels (µg/L)

All Cities

All Colorado cities ranked by chromium-6 level

#	City	Level	Detected?	Violations	Grade
1	Castle Rock	1.30 µg/L	Detected	20	F
2	Aurora	1.20 µg/L	Detected	22	F
3	Thornton	1.00 µg/L	Detected	3	F
4	Colorado Springs	0.89 µg/L	Detected	117	F
5	Brighton	0.75 µg/L	Detected	18	F
6	Commerce City	0.73 µg/L	Detected	0	A
7	Federal Heights	0.56 µg/L	Detected	0	B+
8	Westminster	0.51 µg/L	Detected	1	D
9	Fountain	0.49 µg/L	Detected	4	F
10	Estes Park	0.46 µg/L	Detected	49	D
11	Crestone	0.41 µg/L	Detected	2	B-
12	Fort Collins	0.35 µg/L	Detected	6	D
13	Boulder	0.34 µg/L	Detected	15	F
14	Vail	0.27 µg/L	Detected	0	A
15	Denver	0.25 µg/L	Detected	104	F
16	Golden	0.25 µg/L	Detected	18	B-
17	Centennial	0.20 µg/L	Detected	18	F
18	Black Hawk	0.17 µg/L	Detected	0	A-
19	Lakewood	0.16 µg/L	Detected	28	F
20	Aspen	0.15 µg/L	Detected	2	D
21	Englewood	0.15 µg/L	Detected	33	D
22	Steamboat Springs	0.15 µg/L	Detected	57	F
23	Windsor	0.14 µg/L	Detected	51	D
24	Arvada	0.12 µg/L	Detected	1	B+
25	Pueblo	0.12 µg/L	Detected	15	F
26	Fort Morgan	0.12 µg/L	Detected	5	A-
27	Sterling	0.12 µg/L	Detected	29	C-
28	Eaton	0.12 µg/L	Detected	1	B-
29	Parker	0.11 µg/L	Detected	4	F
30	Palmer Lake	0.11 µg/L	Detected	15	D
31	Empire	0.10 µg/L	Detected	14	C+
32	Trinidad	0.09 µg/L	Detected	12	D
33	Superior	0.09 µg/L	Detected	5	A
34	Lucerne	0.09 µg/L	Detected	0	B+
35	Monument	0.09 µg/L	Detected	23	F
36	Glenwood Springs	0.08 µg/L	Detected	17	F
37	Akron	0.08 µg/L	Detected	4	B
38	Pagosa Springs	0.08 µg/L	Detected	25	F
39	Broomfield	0.07 µg/L	Detected	5	B
40	Clifton	0.07 µg/L	Detected	2	A
41	Usaf Academy	0.07 µg/L	Detected	3	A
42	Evergreen	0.07 µg/L	Detected	57	F
43	Gunnison	0.07 µg/L	Detected	14	C
44	Grand Junction	0.07 µg/L	Detected	4	B
45	Longmont	0.06 µg/L	Detected	2	A-
46	Berthoud	0.06 µg/L	Detected	8	C+
47	Canon City	0.06 µg/L	Detected	4	B+
48	Louisville	0.06 µg/L	Detected	2	A-
49	Breckenridge	0.05 µg/L	Detected	4	B+
50	Evans	0.05 µg/L	Detected	0	B+
51	Greeley	0.05 µg/L	Detected	16	F
52	Lafayette	0.05 µg/L	Detected	19	F
53	Niwot	0.05 µg/L	Detected	1	A
54	Pueblo West	0.05 µg/L	Detected	5	B-
55	Loveland	0.04 µg/L	Detected	50	F
56	Durango	0.04 µg/L	Detected	112	F
57	Erie	0.04 µg/L	Detected	1	A
58	Dolores	0.04 µg/L	Detected	1	B
59	Florence	0.04 µg/L	Detected	2	C+
60	Northglenn	0.04 µg/L	Detected	0	A+
61	Highlands Ranch	0.04 µg/L	Detected	0	B-
62	Wellington	0.03 µg/L	Detected	4	B-

FAQ

Frequently asked questions about chromium-6 in Colorado

Is chromium-6 in Colorado 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. 62 cities in Colorado 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 Colorado 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 Colorado?

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).

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