Drinking Water Notification Levels

Notification levels are health-based advisory levels established by the Division of Drinking Water (DDW) for chemicals in drinking water that lack maximum contaminant levels (MCLs). When chemicals are found at concentrations greater than their notification levels, certain requirements and recommendations apply. The level at which DDW recommends removal of a drinking water source from service is called the "response level."

Since the early 1980s, notification levels (known as "action levels" through 2004) for 93 contaminants have been established. Of those, 40 have gone through the formal regulatory process and now have MCLs.

Currently there are 31 chemicals with notification levels. In addition, another 24 chemicals have archived advisory levels. The complete overview can be found here.

Statutory Requirements

State law (Health and Safety §116455) requires timely notification by drinking water systems whenever a notification level is exceeded in drinking water that is provided to consumers.

The law’s notification requirements apply to:
  • wholesale water systems, who must notify their governing bodies and the water systems that are directly supplied with that drinking water.
  • retail water systems, who must notify their governing bodies and the governing bodies of any local agencies (i.e., city or county, or a city and county) whose jurisdictions include areas supplied with their drinking water.
  • wholesale and retail water systems regulated by the California Public Utilities Commission, who must also notify the commission.

Recommendations from DDW

If a chemical concentration is greater than its notification level in drinking water that is provided to consumers, DDW recommends that the utility inform its customers and consumers about the presence of the chemical, and about health concerns associated with exposure to it. To provide consumer notice, the utility may want to consider using its annual Consumer Confidence Report, a separate mailing, or other method.


If a chemical is present in drinking water that is provided to consumers at concentrations considerably greater than the notification level, DDW recommends that the drinking water system take the source out of service. The level prompting a recommendation for source removal is the "response level" of Health and Safety Code §116455, and depends upon the toxicological endpoint that is the basis for the notification level.

For chemicals with a non-cancer toxicological endpoint, this recommendation occurs at 10 times the notification level.

For four chemicals considered to pose a cancer risk—RDX, TBA, and TNT—this response level recommendation occurs at 100 times the notification level, which is established at a de minimis risk level (a theoretical lifetime risk level of 1 X 10-6, or up to one excess case of cancer per million people exposed daily for 70 years). Thus, the response level for these chemicals corresponds to a lifetime cancer risk of 1 X 10-4. The 10-4 value is at the upper end of the 10-6 to 10-4 cancer risk range. Exposures to environmental chemicals resulting in risks within the 10-6 to 10-4 range are generally considered by public health and environmental regulatory agencies to be "acceptable."

When the notification level for chemicals considered to pose a cancer risk is set at higher than the 1 X 10-6 risk, the response level—still at the 1 X 10-4 risk—occurs at a lower multiple of the notification level: For 1,4-dioxane, this recommendation occurs at 35 times the notification level, and for the nitrosamines NDEA, NDMA, and NDPA this recommendation occurs at 10, 30, and 50 times the notification level, respectively.


When a drinking water system does not take a source out of service despite the presence of a contaminant in drinking water at a level confirmed to be greater than the response level, DDW recommends the following:

  • Notification of the local governing body (i.e., city council or board of supervisors, or both) that indicates water is being provided that exceeds the chemical's response level, and the reason for the continued use of the source.
  • Notification of the water system's customers and other water consumers that the contaminant is present in their drinking water at a concentration greater than its response level, the level at which source removal is recommended by DDW, and the reason for the continued use of the source.
  • Whenever such a public "right-to-know" notice occurs, it should be provided to customers and to the water-consuming population in the affected area that would not directly receive such information, including renters, workers and students.
  • Notification should be provided directly to consumers, for example by posted notices, hand-delivered notices, and water bill inserts.
  • A press release from the water system should also be issued to the local media.
  • Thereafter, DDW recommends the following: (1) Monthly sampling and analysis of the drinking water supply for as long as the contaminant exceeds its response level, and quarterly sampling for 12 months, should the concentration drop below the response level. (2) Quarterly notification of the water system's customers and other water consumers for as long as the contaminant is present at a concentration greater than its response level, using the methods described above. 

    NOTE: Should the water system refuse to provide additional consumer notification, DDW may provide that notification

Additional Information

Information for Drinking Water Systems

More on Chemical Contaminants in Drinking Water