Manganese Contamination

Manganese in Washington Drinking Water

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

Cities Tested

Over SMCL

29%

% Over SMCL

80.5 µg/L

State Avg

▲ 11% vs national

vs National

261

Health Violations

Analysis

Manganese in Washington: what the data shows

Washington has 90 cities with manganese data from the EPA's UCMR 4 program (2018–2020). Manganese exceeded the 50 µg/L EPA secondary MCL in 26 of those cities. The state average max detected level is 80.5 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

Washington

29%

26 of 90 cities

→ ▲ 11% above national rate (worse)

National avg

18%

729 of 4068 cities

City Map

Manganese data across Washington

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 Washington

Highest Manganese levels (µg/L)

All Cities

All Washington cities ranked by manganese level

#	City	Level	Over SMCL?	Violations	Grade
1	Grandview	1590.0 µg/L	Over SMCL	5	D+
2	Marysville	1403.0 µg/L	Over SMCL	12	D
3	Poulsbo	1178.0 µg/L	Over SMCL	95	F
4	Federal Way	240.0 µg/L	Over SMCL	2	B
5	Olympia	178.0 µg/L	Over SMCL	66	F
6	Pullman	174.0 µg/L	Over SMCL	0	B+
7	Vashon	140.0 µg/L	Over SMCL	24	F
8	Spanaway	139.1 µg/L	Over SMCL	9	C+
9	Vancouver	130.0 µg/L	Over SMCL	36	F
10	Sammamish	110.0 µg/L	Over SMCL	6	C-
11	Bainbridge Island	108.0 µg/L	Over SMCL	3	A
12	Kent	107.0 µg/L	Over SMCL	31	F
13	Joint Base Lewis-Mcchord	105.0 µg/L	Over SMCL	3	B+
14	Tacoma	101.6 µg/L	Over SMCL	232	F
15	Moses Lake	100.0 µg/L	Over SMCL	132	F
16	Bremerton	90.0 µg/L	Over SMCL	13	C
17	Silverdale	90.0 µg/L	Over SMCL	17	F
18	Lakewood	85.0 µg/L	Over SMCL	5	B+
19	Tekoa	83.0 µg/L	Over SMCL	5	C
20	Puyallup	80.6 µg/L	Over SMCL	124	F
21	Lacey	71.6 µg/L	Over SMCL	125	F
22	Clinton	71.0 µg/L	Over SMCL	8	C
23	Issaquah	66.9 µg/L	Over SMCL	10	C-
24	Cheney	61.9 µg/L	Over SMCL	5	A-
25	Enumclaw	56.5 µg/L	Over SMCL	1	B+
26	Sunnyside	52.2 µg/L	Over SMCL	2	A-
27	Moxee	38.0 µg/L	No	2	B
28	Stanwood	37.9 µg/L	No	31	D
29	Port Orchard	37.0 µg/L	No	753	F
30	Yakima	36.5 µg/L	No	162	F
31	Selah	35.6 µg/L	No	4	B
32	Westport	35.0 µg/L	No	4	D+
33	Snohomish	27.6 µg/L	No	11	D
34	Mercer Island	24.0 µg/L	No	1	A-
35	Buckley	22.5 µg/L	No	5	D+
36	West Richland	21.0 µg/L	No	99	F
37	Aberdeen	21.0 µg/L	No	10	D
38	Auburn	19.9 µg/L	No	18	D+
39	Edmonds	18.0 µg/L	No	0	A-
40	Maple Valley	17.0 µg/L	No	7	C+
41	Shelton	15.5 µg/L	No	158	F
42	Tumwater	14.2 µg/L	No	24	D+
43	Lynnwood	13.0 µg/L	No	0	B-
44	Pasco	12.9 µg/L	No	137	D
45	Arlington	11.3 µg/L	No	83	F
46	Clarkston	11.2 µg/L	No	16	B+
47	Mount Vernon	9.8 µg/L	No	191	F
48	Oak Harbor	9.7 µg/L	No	105	F
49	Fircrest	9.4 µg/L	No	4	A-
50	Kennewick	8.9 µg/L	No	78	F
51	Ellensburg	8.9 µg/L	No	19	D
52	Nas Whidbey Island	7.8 µg/L	No	0	A+
53	Centralia	7.3 µg/L	No	5	B-
54	Seattle	6.5 µg/L	No	138	F
55	Woodinville	6.4 µg/L	No	1	A-
56	Battle Ground	6.2 µg/L	No	12	B-
57	Bothell	5.8 µg/L	No	7	F
58	Burien	5.7 µg/L	No	1	B+
59	Renton	5.3 µg/L	No	11	D+
60	Hoquiam	5.1 µg/L	No	6	B-
61	Bellevue	4.2 µg/L	No	2	A
62	Mukilteo	4.2 µg/L	No	0	A-
63	Newcastle	4.2 µg/L	No	1	A
64	Dupont	3.8 µg/L	No	0	A
65	East Wenatchee	3.6 µg/L	No	19	B
66	Monroe	3.2 µg/L	No	4	C
67	Snoqualime	3.2 µg/L	No	4	A-
68	Mountlake Terrace	3.0 µg/L	No	0	B+
69	Mead	2.8 µg/L	No	3	B-
70	Spokane Valley	2.4 µg/L	No	10	C-
71	Duvall	2.4 µg/L	No	0	A-
72	Everett	2.2 µg/L	No	16	D
73	Chehalis	2.1 µg/L	No	12	F
74	Redmond	2.0 µg/L	No	4	B-
75	Bellingham	2.0 µg/L	No	54	F
76	Longview	2.0 µg/L	No	0	B+
77	Kirkland	1.9 µg/L	No	4	D+
78	Lynden	1.8 µg/L	No	235	F
79	Shoreline	1.5 µg/L	No	0	A-
80	Richland	1.4 µg/L	No	7	C+
81	Greenacres	1.4 µg/L	No	12	B+
82	Sequim	1.2 µg/L	No	64	F
83	Kenmore	0.8 µg/L	No	0	B-
84	Port Angeles	0.7 µg/L	No	19	F
85	Spokane	0.7 µg/L	No	56	F
86	Port Townsend	0.5 µg/L	No	15	F
87	Ferndale	0.5 µg/L	No	110	F
88	Washougal	0.5 µg/L	No	2	B+
89	Liberty Lake	0.4 µg/L	No	2	A
90	Walla Walla	0.4 µg/L	No	84	D

FAQ

Frequently asked questions about manganese in Washington

Is manganese in Washington tap water harmful?

The EPA secondary MCL for manganese is 50 µg/L, set primarily for aesthetic reasons (taste, color, staining). 26 cities in Washington 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 Washington 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.

More contaminants