Nitrate Contamination

Nitrate in Wisconsin Drinking Water

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

210

Cities Tested

210

Has Violations

100%

% Has Violations

4.5 violations

State Avg

▼ 0% vs national

vs National

388

Health Violations

Analysis

Nitrate in Wisconsin: what the data shows

Wisconsin has 210 cities with nitrate-related violations. The EPA MCL for nitrate is 10 mg/L (measured as nitrogen). The state has 210 cities with at least one nitrate violation. Nitrate is the most common groundwater contaminant in the United States. It enters water supplies primarily through agricultural fertilizer runoff, septic system leaching, and animal feedlot operations. Rural and agricultural communities face the highest risk. The primary acute health concern is methemoglobinemia ("blue baby syndrome") in infants under six months. Emerging research also links chronic nitrate exposure to thyroid disease, certain cancers, and adverse birth outcomes. Reverse osmosis, ion exchange, and distillation can remove nitrate from drinking water — standard carbon filters do not.

Comparison

Cities exceeding 10 mg/L EPA MCL

Wisconsin

100%

210 of 210 cities

← = Exactly at national rate

National avg

100%

8001 of 8001 cities

City Map

Nitrate data across Wisconsin

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

Worst Offenders

Top 10 cities by nitrate level in Wisconsin

Highest Nitrate levels (violations)

All Cities

All Wisconsin cities ranked by nitrate level

#	City	Level	Violations?	Violations	Grade
1	Thiensville	50 violations	Yes	30	D
2	Twin Lakes	30 violations	Yes	29	F
3	Menomonie	23 violations	Yes	30	F
4	Muskego	21 violations	Yes	36	D
5	Crandon	21 violations	Yes	8	D+
6	Lake Geneva	19 violations	Yes	24	C
7	Hayward	18 violations	Yes	19	F
8	Mauston	18 violations	Yes	17	F
9	Pewaukee	17 violations	Yes	71	F
10	River Falls	17 violations	Yes	14	C+
11	Stevens Point	16 violations	Yes	14	C+
12	Mosinee	14 violations	Yes	15	F
13	Delafield	14 violations	Yes	22	D
14	West Bend	13 violations	Yes	11	F
15	Chetek	13 violations	Yes	6	C+
16	Kenosha	12 violations	Yes	11	D
17	Mequon	12 violations	Yes	21	F
18	Edgerton	12 violations	Yes	17	D
19	Evansville	12 violations	Yes	25	C-
20	Wales	12 violations	Yes	7	C+
21	Chippewa Falls	11 violations	Yes	12	D+
22	Union Grove	11 violations	Yes	26	D
23	Poynette	11 violations	Yes	11	D
24	Fontana	11 violations	Yes	8	B-
25	Eau Claire	10 violations	Yes	18	D+
26	Holmen	10 violations	Yes	5	B-
27	La Crosse	9 violations	Yes	34	F
28	Waunakee	9 violations	Yes	11	B-
29	Delavan	9 violations	Yes	6	F
30	Ladysmith	9 violations	Yes	18	D
31	Campbellsport	9 violations	Yes	5	C+
32	Janesville	8 violations	Yes	12	B
33	Brookfield	8 violations	Yes	32	C-
34	New Berlin	8 violations	Yes	14	B
35	Williams Bay	8 violations	Yes	1	C
36	Spring Green	8 violations	Yes	14	C
37	Fond Du Lac	7 violations	Yes	51	F
38	Plymouth	7 violations	Yes	8	C+
39	New London	7 violations	Yes	2	D+
40	Elm Grove	7 violations	Yes	28	F
41	Whitewater	6 violations	Yes	22	C+
42	Plover	6 violations	Yes	9	B+
43	New Richmond	6 violations	Yes	15	B
44	Prairie Du Sac	6 violations	Yes	12	C+
45	Spooner	6 violations	Yes	21	B
46	Odanah	6 violations	Yes	2	D+
47	Wautoma	6 violations	Yes	0	A
48	Clinton	6 violations	Yes	4	B-
49	Bristol	6 violations	Yes	10	B
50	Trempealeau	6 violations	Yes	5	A
51	Montreal	6 violations	Yes	10	B-
52	Arlington	6 violations	Yes	7	B
53	Hartford	5 violations	Yes	2	B+
54	Verona	5 violations	Yes	1	B+
55	Black River Falls	5 violations	Yes	11	D+
56	Burlington	5 violations	Yes	27	B-
57	Antigo	5 violations	Yes	8	F
58	Bloomer	5 violations	Yes	11	B+
59	Boscobel	5 violations	Yes	7	A-
60	Rio	5 violations	Yes	1	B+
61	Madison	4 violations	Yes	14	F
62	Beloit	4 violations	Yes	2	B+
63	Weston	4 violations	Yes	0	B+
64	Stoughton	4 violations	Yes	4	B+
65	Reedsburg	4 violations	Yes	1	B+
66	Columbus	4 violations	Yes	8	B
67	Medford	4 violations	Yes	9	C+
68	Minocqua	4 violations	Yes	4	C-
69	Neillsville	4 violations	Yes	7	C+
70	Walworth	4 violations	Yes	8	B-
71	Cumberland	4 violations	Yes	5	A
72	Galesville	4 violations	Yes	3	C
73	Reeseville	4 violations	Yes	3	B-
74	Eleva	4 violations	Yes	5	D
75	Iron River	4 violations	Yes	11	C+
76	South Wayne	4 violations	Yes	13	A-
77	Bay City	4 violations	Yes	3	A-
78	Superior	3 violations	Yes	17	F
79	Franklin	3 violations	Yes	10	B
80	Hudson	3 violations	Yes	4	B
81	Platteville	3 violations	Yes	11	D+
82	Keshena	3 violations	Yes	6	C+
83	Prescott	3 violations	Yes	8	B+
84	Fox Lake	3 violations	Yes	6	B
85	Bowler	3 violations	Yes	8	A-
86	Dousman	3 violations	Yes	12	C
87	Bayfield	3 violations	Yes	7	C
88	Schofield	3 violations	Yes	2	B
89	Augusta	3 violations	Yes	2	D+
90	Owen	3 violations	Yes	5	C-
91	Loyal	3 violations	Yes	2	A-
92	Reedsville	3 violations	Yes	5	B+
93	Clear Lake	3 violations	Yes	1	A
94	Elk Mound	3 violations	Yes	4	B+
95	Balsam Lake	3 violations	Yes	4	A
96	Arena	3 violations	Yes	5	C-
97	Pittsville	3 violations	Yes	1	A-
98	Merrimac	3 violations	Yes	6	B+
99	Boyd	3 violations	Yes	3	A
100	Waukesha	2 violations	Yes	320	D
101	Oak Creek	2 violations	Yes	5	B
102	Menomonee Falls	2 violations	Yes	6	B+
103	Oregon	2 violations	Yes	12	D+
104	Two Rivers	2 violations	Yes	5	C-
105	Elkhorn	2 violations	Yes	19	F
106	Merrill	2 violations	Yes	7	C-
107	Hartland	2 violations	Yes	8	B
108	Rice Lake	2 violations	Yes	17	F
109	Mukwonago	2 violations	Yes	27	D
110	Rhinelander	2 violations	Yes	5	B
111	Prairie Du Chien	2 violations	Yes	9	B
112	East Troy	2 violations	Yes	1	B
113	Chilton	2 violations	Yes	8	B+
114	Marshall	2 violations	Yes	3	A
115	Arcadia	2 violations	Yes	0	A+
116	Seymour	2 violations	Yes	2	A-
117	Somerset	2 violations	Yes	10	B-
118	Genoa City	2 violations	Yes	15	B-
119	Winneconne	2 violations	Yes	17	C
120	New Glarus	2 violations	Yes	1	A-
121	Pardeeville	2 violations	Yes	5	A
122	Eagle	2 violations	Yes	27	B+
123	Durand	2 violations	Yes	0	A
124	Randolph	2 violations	Yes	7	B
125	Thorp	2 violations	Yes	3	D+
126	Sharon	2 violations	Yes	6	C-
127	Muscoda	2 violations	Yes	5	A
128	Blair	2 violations	Yes	2	A-
129	Laona	2 violations	Yes	19	D+
130	Oakfield	2 violations	Yes	0	A
131	Boyceville	2 violations	Yes	2	A-
132	Valders	2 violations	Yes	3	A-
133	Plainfield	2 violations	Yes	0	A
134	Centuria	2 violations	Yes	0	A-
135	Footville	2 violations	Yes	1	A-
136	Stoddard	2 violations	Yes	7	B+
137	Cambria	2 violations	Yes	2	A
138	Whitelaw	2 violations	Yes	1	B-
139	Wauzeka	2 violations	Yes	0	A
140	Merrillan	2 violations	Yes	1	B+
141	Minong	2 violations	Yes	0	A
142	New Auburn	2 violations	Yes	13	A
143	Adell	2 violations	Yes	1	A-
144	Green Bay	1 violations	Yes	74	D+
145	Sun Prairie	1 violations	Yes	4	A
146	Fitchburg	1 violations	Yes	0	A
147	Watertown	1 violations	Yes	10	D
148	Germantown	1 violations	Yes	8	B-
149	Marshfield	1 violations	Yes	9	C-
150	Onalaska	1 violations	Yes	2	A-
151	Kaukauna	1 violations	Yes	9	B+
152	Beaver Dam	1 violations	Yes	11	A-
153	Port Washington	1 violations	Yes	6	B+
154	Baraboo	1 violations	Yes	0	B
155	Grafton	1 violations	Yes	12	C+
156	Sussex	1 violations	Yes	70	D+
157	Cedarburg	1 violations	Yes	1	B+
158	Portage	1 violations	Yes	9	B
159	Altoona	1 violations	Yes	15	C+
160	Tomah	1 violations	Yes	18	B+
161	Mount Horeb	1 violations	Yes	1	A
162	Waupaca	1 violations	Yes	3	B-
163	Oneida	1 violations	Yes	3	D
164	Mayville	1 violations	Yes	6	A-
165	Suamico	1 violations	Yes	1	A
166	Kewaskum	1 violations	Yes	0	A
167	Kiel	1 violations	Yes	3	A-
168	Horicon	1 violations	Yes	10	B+
169	Wisconsin Dells	1 violations	Yes	18	F
170	Johnson Creek	1 violations	Yes	7	C
171	Ellsworth	1 violations	Yes	6	B+
172	Lake Delton	1 violations	Yes	2	A-
173	Algoma	1 violations	Yes	2	A-
174	New Holstein	1 violations	Yes	2	A-
175	Oconto Falls	1 violations	Yes	4	B+
176	Osceola	1 violations	Yes	8	B
177	Lomira	1 violations	Yes	7	B+
178	Abbotsford	1 violations	Yes	2	B
179	Belgium	1 violations	Yes	2	A-
180	Whitehall	1 violations	Yes	2	B
181	North Prairie	1 violations	Yes	1	B+
182	Webster	1 violations	Yes	13	B+
183	Cambridge	1 violations	Yes	8	B
184	Oxford	1 violations	Yes	2	B
185	Fall Creek	1 violations	Yes	20	B
186	Montello	1 violations	Yes	9	B-
187	Hillsboro	1 violations	Yes	13	C+
188	Hazel Green	1 violations	Yes	14	F
189	Frederic	1 violations	Yes	0	A-
190	Wittenberg	1 violations	Yes	0	A+
191	Green Lake	1 violations	Yes	5	B-
192	Strum	1 violations	Yes	5	B+
193	Crivitz	1 violations	Yes	2	A-
194	Benton	1 violations	Yes	1	A
195	Paddock Lake	1 violations	Yes	2	B
196	Lone Rock	1 violations	Yes	3	A-
197	Brandon	1 violations	Yes	6	A-
198	Highland	1 violations	Yes	2	A
199	Birnamwood	1 violations	Yes	2	A
200	Ixonia	1 violations	Yes	16	D+
201	Wabeno	1 violations	Yes	1	A
202	Almena	1 violations	Yes	0	A
203	Ridgeway	1 violations	Yes	6	A-
204	Avoca	1 violations	Yes	2	B+
205	Bruce	1 violations	Yes	6	A
206	La Valle	1 violations	Yes	16	B-
207	Hales Corners	1 violations	Yes	6	C+
208	Wausaukee	1 violations	Yes	2	B
209	Land O Lakes	1 violations	Yes	7	C-
210	Warrens	1 violations	Yes	6	A-

FAQ

Frequently asked questions about nitrate in Wisconsin

Is nitrate in Wisconsin tap water dangerous?

Yes — 210 cities in Wisconsin have nitrate-related violations. The EPA MCL is 10 mg/L. Nitrate is especially dangerous for infants under six months, where it can cause methemoglobinemia ("blue baby syndrome"). Adults face lower acute risk, but chronic exposure is linked to thyroid disease and certain cancers.

How can I remove nitrate from my drinking water?

Reverse osmosis, ion exchange, and distillation are effective at removing nitrate. Standard carbon filters (including most pitcher and faucet-mount filters) do NOT remove nitrate. If you rely on a private well in an agricultural area, have your water tested annually for nitrate.

What causes high nitrate levels in Wisconsin water?

Nitrate contamination comes primarily from agricultural fertilizer runoff, septic system leaching, and animal feedlot operations. Rural communities near intensive farming are most at risk. Shallow wells are particularly vulnerable. Heavy rainfall can spike nitrate levels as it washes fertilizer into groundwater and surface water supplies.

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