Arsenic Contamination

Arsenic in California Drinking Water

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

208

Cities Tested

208

Has Violations

100%

% Has Violations

24.5 violations

State Avg

▼ 0% vs national

vs National

620

Health Violations

Analysis

Arsenic in California: what the data shows

California has 208 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 208 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

California

100%

208 of 208 cities

← = Exactly at national rate

National avg

100%

5270 of 5270 cities

City Map

Arsenic data across California

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 California

Highest Arsenic levels (violations)

All Cities

All California cities ranked by arsenic level

#	City	Level	Violations?	Violations	Grade
1	Madera	284 violations	Yes	564	D
2	Bakersfield	260 violations	Yes	690	F
3	Lancaster	170 violations	Yes	204	D
4	Rosamond	169 violations	Yes	205	F
5	Salinas	164 violations	Yes	639	F
6	Oakhurst	159 violations	Yes	198	D
7	Hanford	150 violations	Yes	197	D+
8	Sacramento	149 violations	Yes	425	F
9	Lake Isabella	145 violations	Yes	162	D+
10	Hughson	131 violations	Yes	139	D+
11	Thermal	122 violations	Yes	127	D
12	North Edwards	107 violations	Yes	119	D
13	Mojave	104 violations	Yes	114	D
14	Los Angeles	91 violations	Yes	94	F
15	Clovis	76 violations	Yes	221	F
16	Rancho Cordova	75 violations	Yes	115	F
17	Brentwood	70 violations	Yes	91	F
18	Santa Rosa	64 violations	Yes	177	F
19	Riverbank	64 violations	Yes	75	D
20	Weldon	63 violations	Yes	193	D+
21	Barstow	63 violations	Yes	66	F
22	Armona	62 violations	Yes	71	B+
23	Boron	62 violations	Yes	60	B+
24	Grimes	61 violations	Yes	61	D
25	Ceres	60 violations	Yes	129	F
26	Oakley	57 violations	Yes	60	D
27	El Monte	56 violations	Yes	79	F
28	Keyes	56 violations	Yes	60	B+
29	Caruthers	56 violations	Yes	63	B-
30	Pixley	53 violations	Yes	59	B
31	Arvin	52 violations	Yes	81	C+
32	Alpaugh	51 violations	Yes	48	B
33	Ludlow	49 violations	Yes	82	D+
34	Delano	48 violations	Yes	67	B
35	Kettleman City	47 violations	Yes	58	C+
36	Encinitas	45 violations	Yes	55	F
37	Firebaugh	45 violations	Yes	89	D
38	Arroyo Grande	44 violations	Yes	93	F
39	Bridgeport	44 violations	Yes	47	B-
40	Los Molinos	43 violations	Yes	50	A-
41	Granite Bay	42 violations	Yes	43	B-
42	Fort Irwin	41 violations	Yes	60	B+
43	Coalinga	40 violations	Yes	267	D
44	Fresno	39 violations	Yes	523	F
45	Isleton	39 violations	Yes	52	C+
46	Lamont	36 violations	Yes	40	B+
47	Blairsden	35 violations	Yes	44	B
48	San Bernardino	31 violations	Yes	192	F
49	Lathrop	31 violations	Yes	44	B
50	Tehachapi	31 violations	Yes	96	F
51	Grover Beach	31 violations	Yes	34	F
52	Junction City	31 violations	Yes	35	A-
53	Manteca	30 violations	Yes	39	B-
54	Livermore	30 violations	Yes	53	B
55	Riverdale	30 violations	Yes	69	B+
56	Laton	30 violations	Yes	49	C+
57	Livingston	29 violations	Yes	29	C-
58	Modesto	28 violations	Yes	76	D
59	Stockton	28 violations	Yes	261	F
60	Tranquillity	27 violations	Yes	37	B
61	Pasadena	24 violations	Yes	92	F
62	Hollister	23 violations	Yes	132	F
63	Royal Oaks	23 violations	Yes	201	D
64	Chowchilla	21 violations	Yes	25	A-
65	Three Rivers	21 violations	Yes	177	F
66	Helendale	21 violations	Yes	22	A-
67	Trona	21 violations	Yes	21	A
68	Watsonville	20 violations	Yes	74	F
69	Lake Forest	20 violations	Yes	38	B-
70	Galt	20 violations	Yes	27	B+
71	Mcfarland	20 violations	Yes	42	C+
72	Klamath	19 violations	Yes	102	D
73	Lemoore	18 violations	Yes	112	D
74	New Cuyama	18 violations	Yes	21	A
75	Portola	16 violations	Yes	71	C-
76	Ridgecrest	15 violations	Yes	26	A-
77	Tule River Reservation	15 violations	Yes	34	D
78	Paso Robles	14 violations	Yes	42	F
79	Wasco	14 violations	Yes	26	B+
80	Earlimart	14 violations	Yes	40	B
81	Laytonville	13 violations	Yes	13	A
82	Live Oak	11 violations	Yes	26	A-
83	Richgrove	11 violations	Yes	24	C
84	Palmdale	10 violations	Yes	15	C+
85	Susanville	10 violations	Yes	34	A-
86	Kernville	10 violations	Yes	38	B-
87	King George	9 violations	Yes	30	D+
88	Santa Ysabel	9 violations	Yes	17	D
89	Pine Mountain Club	9 violations	Yes	9	A-
90	Felton	9 violations	Yes	21	C
91	Lompoc	8 violations	Yes	18	C
92	Anza	8 violations	Yes	53	F
93	Indio	7 violations	Yes	12	F
94	Woodland	7 violations	Yes	52	F
95	Adelanto	7 violations	Yes	13	C
96	Shafter	7 violations	Yes	25	A-
97	Frazier Park	7 violations	Yes	56	C+
98	Lost Hills	7 violations	Yes	13	A
99	Le Grand	7 violations	Yes	15	B-
100	Pacific Grove	6 violations	Yes	15	B-
101	Rancho Santa Fe	6 violations	Yes	3	A-
102	Needles	6 violations	Yes	45	F
103	Sebastopol	6 violations	Yes	18	B-
104	Meadview	6 violations	Yes	16	B
105	Meadview	6 violations	Yes	16	B
106	South Lake Tahoe	5 violations	Yes	15	C
107	Springville	5 violations	Yes	82	D+
108	Trinidad	5 violations	Yes	30	D
109	Riverside	4 violations	Yes	13	C
110	Redding	4 violations	Yes	49	F
111	Tracy	4 violations	Yes	45	C
112	Elk Grove	4 violations	Yes	28	C
113	Valley Center	4 violations	Yes	15	F
114	Norco	4 violations	Yes	39	F
115	Oakdale	4 violations	Yes	34	C-
116	South Pasadena	4 violations	Yes	5	A
117	Chico	4 violations	Yes	306	F
118	Blythe	4 violations	Yes	143	D
119	West Covina	4 violations	Yes	25	F
120	St. Helena	4 violations	Yes	29	C+
121	Laguna Beach	3 violations	Yes	2	B
122	Petaluma	3 violations	Yes	2	B
123	Truckee	3 violations	Yes	7	A-
124	Julian	3 violations	Yes	22	D
125	Colusa	3 violations	Yes	6	C-
126	Pauma Valley	3 violations	Yes	88	F
127	San Francisco	3 violations	Yes	100	F
128	Irvine	2 violations	Yes	84	F
129	Santa Barbara	2 violations	Yes	52	F
130	Turlock	2 violations	Yes	16	B-
131	Yuba City	2 violations	Yes	24	A-
132	Lodi	2 violations	Yes	16	C+
133	Rohnert Park	2 violations	Yes	21	F
134	Oroville	2 violations	Yes	7	C-
135	Imperial	2 violations	Yes	36	C+
136	Marysville	2 violations	Yes	11	B+
137	Westlake Village	2 violations	Yes	8	F
138	Willits	2 violations	Yes	23	C-
139	Alpine	2 violations	Yes	25	C-
140	Gridley	2 violations	Yes	4	B
141	Buellton	2 violations	Yes	2	B+
142	Denair	2 violations	Yes	3	A
143	Hoopa	2 violations	Yes	16	B+
144	Strathmore	2 violations	Yes	118	D+
145	Valley Springs	2 violations	Yes	2	A
146	Gerber	2 violations	Yes	5	B
147	Campo	2 violations	Yes	74	D
148	Madison	2 violations	Yes	6	D+
149	Corona Del Mar	2 violations	Yes	3	C-
150	Saugus	2 violations	Yes	11	A
151	San Jose	1 violations	Yes	142	F
152	San Diego	1 violations	Yes	43	F
153	Long Beach	1 violations	Yes	2	C
154	Alhambra	1 violations	Yes	7	A-
155	Palm Desert	1 violations	Yes	12	C+
156	Spring Valley	1 violations	Yes	4	B
157	Oxnard	1 violations	Yes	49	F
158	Concord	1 violations	Yes	19	B-
159	Corona	1 violations	Yes	81	D
160	Sunnyvale	1 violations	Yes	3	A
161	Orange	1 violations	Yes	3	B
162	Fairfield	1 violations	Yes	7	B-
163	Santa Maria	1 violations	Yes	36	F
164	Porterville	1 violations	Yes	74	F
165	Montebello	1 violations	Yes	5	B
166	Beverly Hills	1 violations	Yes	18	B
167	Sonora	1 violations	Yes	25	D+
168	San Andreas	1 violations	Yes	17	B-
169	Sanger	1 violations	Yes	16	C
170	Port Hueneme	1 violations	Yes	0	B+
171	Sutter Creek	1 violations	Yes	7	B+
172	Red Bluff	1 violations	Yes	23	F
173	Ripon	1 violations	Yes	10	A-
174	Pala	1 violations	Yes	30	C-
175	Sonoma	1 violations	Yes	5	B-
176	Newman	1 violations	Yes	3	A-
177	Calimesa	1 violations	Yes	6	B
178	Rio Vista	1 violations	Yes	3	A+
179	Georgetown	1 violations	Yes	4	B+
180	Forestville	1 violations	Yes	14	B-
181	La Canada	1 violations	Yes	5	B
182	Santa Ynez	1 violations	Yes	14	A-
183	Fowler	1 violations	Yes	2	A
184	Calistoga	1 violations	Yes	15	C+
185	Carnelian Bay	1 violations	Yes	15	B
186	Murphys	1 violations	Yes	11	B+
187	Havasu Lake	1 violations	Yes	37	D
188	Los Gatos	1 violations	Yes	138	D
189	Sutter	1 violations	Yes	6	A
190	Smith River	1 violations	Yes	11	C+
191	San Juan Bautista	1 violations	Yes	18	C+
192	Pine Grove	1 violations	Yes	17	B
193	Cabazon	1 violations	Yes	5	A-
194	Inyokern	1 violations	Yes	21	D
195	Point Reyes Station	1 violations	Yes	0	A-
196	Bethel Island	1 violations	Yes	12	C+
197	Upper Lake	1 violations	Yes	4	B
198	Redwood Valley	1 violations	Yes	2	C
199	Saratoga	1 violations	Yes	7	B+
200	Baker	1 violations	Yes	1	B+
201	Wadsworth, Nv	1 violations	Yes	2	D+
202	Wadsworth, Nv	1 violations	Yes	2	D+
203	Nixon	1 violations	Yes	2	C-
204	Nixon	1 violations	Yes	2	C-
205	Los Altos	1 violations	Yes	13	B
206	Palo Verde	1 violations	Yes	7	C
207	Stinson Beach	1 violations	Yes	2	A-
208	Lone Pine Reservation	1 violations	Yes	6	A-

FAQ

Frequently asked questions about arsenic in California

Is arsenic in California tap water a concern?

Yes — 208 cities in California 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 California?

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 California 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.

More contaminants