Arsenic MCL Revision
Rulemaking Status
This rulemaking is in development and has not yet begun.
Inquiries regarding the contents of this regulation may be directed to DDWRegUnit@waterboards.ca.gov.
Background
More information about arsenic.
The current arsenic MCL (maximum contaminant level) is 10 µg/L (0.01 mg/L).
The current arsenic DLR (detection limit for purposes of reporting) is 2 µg/L (0.002 mg/L).
The current arsenic PHG (public health goal) is 0.004 µg/L (0.000004 mg/L).
Occurrence
The tables below summarize the Division of Drinking Water's water quality database's reported findings of arsenic from 1 January 2014 to 1 November 2024 for community water systems (CWS), non-community non-transient water systems (NTNCWS), and transient non-community water systems (TNCWS) using the highest running annual average for each source. In this case, sources are active wells, springs, infiltration galleries, common headers, and other intakes reporting monitoring results for arsenic. Data includes both raw and treated sources.
| Highest Running Annual Average Source Concentration (µg/L) | CWS | NTNCWS | TNCWS | |||
|---|---|---|---|---|---|---|
| No. of Sources | No. of Systems | No. of Sources | No. of Systems | No. of Sources | No. of Systems | |
| ≤ 2 (DLR) | 4,745 | 1,678 | 873 | 673 | 240 | 208 |
| > 2 and ≤ 4 | 1,915 | 842 | 440 | 370 | 64 | 61 |
| > 4 and ≤ 6 | 701 | 402 | 208 | 182 | 23 | 22 |
| > 6 and ≤ 8 | 392 | 264 | 106 | 93 | 16 | 16 |
| > 8 and ≤ 10 | 257 | 181 | 74 | 68 | 12 | 12 |
| > 10 (MCL) | 624 | 338 | 227 | 189 | 71 | 66 |
| Total Tested | 8,634 | 2,558 | 1,928 | 1,397 | 426 | 373 |
| Statewide Total | 9,583 | 2,640 | 2,115 | 1,446 | 3,538 | 2,941 |
| Percent Tested | 90.1% | 96.9% | 91.2% | 96.6% | 12.0% | 12.7% |
The values above should not be considered to reflect arsenic in drinking water served to customers, since water from these sources may be blended, treated, or otherwise not used to provide drinking water. For more information about the quality of specific drinking water supplies, see public water systems' annual Consumer Confidence Reports. The sampling results in the table above were obtained from laboratories using one of the following ELAP accredited methods:
- SM 3113 B: Metals by Electrothermal Atomic Absorption Spectrometry (2010)
- EPA Method 200.8: Determination of Trace Elements in Water and Wastes by Inductively Coupled Plasma – Mass Spectrometry (1994)
- EPA Method 200.9: Determination of Trace Elements by Stabilized Temperature Graphic Furnace Atomic Absorption (1994)
Rulemaking Proceedings
- Notice of Proposed Rulemaking Published: TBD
- Close of the 45-Day Public Comment Period: TBD
- Date of Scheduled Public Hearings: TBD
- Date filed with Office of Administrative Law: TBD
- Approved by Office of Administrative Law: TBD
- Filed with the Secretary of State: TBD
- Effective Date: TBD
Sections Affected
- California Code of Regulations, Title 22, sections 64431, 64432, 64447.2, 64465, 64481, and 64482.D
Rulemaking File
- TBD
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Contact Us
State Water Resources Control Board
Division of Drinking Water
Regulatory Development Unit
Mailing Address:
P.O. Box 100
Sacramento, CA 95812-0100
Street Address:
1001 I Street
Sacramento, CA 95814
E-mail us at DDWRegUnit@waterboards.ca.gov.
