Chemicals and Contaminants in Drinking Water

Last Update: December 22, 2009

Regulated Contaminants

• Drinking water standards are called maximum contaminant levels (MCLs).  Primary MCLs address health concerns -- here is a comparison of federal and California MCLs (PDF). MCLs are found in Title 22 of the California Code of Regulations.  (Go to Drinking Water Regulations and Statutes).
• Esthetics such as taste and odor are addressed by secondary MCLs (PDF). 
• Here is the process for establishing MCLs in California.
• Learn about MCLs and public health goals (PHGs).
• Standards also include Detection Limits for purposes of Reporting (DLRs), included in this list of chemicals and characteristics (Excel)associated with the submittal of analytical results by electronic data transfer (EDT).
• Also, see chemical-specific information on arsenic, chromium-6 (currently regulated under the total chromium MCL), manganese (which has a secondary MCL), MTBE, nitrate and nitrite, and perchlorate; and information about fluoridation by public water systems.

Public Notification and Information about Contaminants

• Water systems: Use these templates -- and contact your CDPH district office (PDF)-- when public notification is required because of chemical or microbiological contamination, or because of other conditions. 
• Consumers:  Information about your drinking water quality is available from your water system in its annual Consumer Confidence Report (CCR). A number of CCRs for California water systems are available on the US EPA's website.

Unregulated Contaminants

• Notification Levels:  CDPH uses these health-based advisory levels for certain chemicals without MCLs. Exceeding them prompts certain requirements and recommendations.

• Also, see chemical-specific information on 1,2,3-trichloropropane and  NDMA and other nitrosamines.

• Unregulated chemicals for which monitoring is required - these regulations were repealed October 18, 2007.

• Emerging contaminants - Information about emerging contaminants is with the FAQs for CDPH's draft recharge reuse water, along with pertinent links.

Use of Extremely Impaired Sources

• CDPH follows Procedure Memorandum 97-005 (PDF) for evaluating of the use of extremely impaired sources for drinking water. 

Treatment Technology

• CDPH's Water Treatment Technology Approval Process (PDF) - January 16, 2002

Sampling and Analysis Issues

• Monitoring schedules
• EDT - data submittal by laboratories
• Additional information for laboratories 
• For extremely impaired sources (PDF) and recycled water analysis and reporting of non-target compounds—including tentatively identified compounds (TICs)—are these documents:  
• Non-Target Volatile Organic Chemicals (PDF) - September 10, 2003 draft.
• Non-Target Semi-Volatile Organic Chemicals (PDF) - September 10, 2003 draft.
• Characterizing Severely Impaired Water Sources through Elemental Analysis (PDF) - January 26, 2004.