Notification Levels for Chemicals in Drinking Water

Notification Levels are health-based advisory levels for chemicals in drinking water that are established for chemicals for which there are no formal regulatory standards (Maximum Contaminant Levels, or MCLs). Notification Levels may be established by the State Water Resources Control Board’s Division of Drinking Water (DDW) when a chemical is found in or threatens drinking water sources. Upon request by DDW, OEHHA performs a risk assessment of the chemical using standard risk and exposure assumptions and proposes a health-protective level. A notification level is then established by DDW, and amended as necessary as conditions or risk assessment methods change. The OEHHA letters to DDW, which provide brief summaries of the toxicological literature and proposed Notification Levels, can be accessed through the links below.

When notification levels are exceeded, the drinking water system is required to notify the local governing body of the local agency in which the users of the drinking water reside. If the notification level is exceeded, the State Water Resources Control Board (SWRCB) recommends that the utility also inform its customers and consumers about the presence of the contaminant and about the health concerns associated with its exposure. Response levels are levels of the contaminant at which SWRCB recommends the drinking water system take the affected water source out of service. These levels range from 10 to 100 times the notification level depending on the chemical. Further information on notification and response levels can be found at the SWRCB Web site. The California legislation covering notification and response levels is Health and Safety Code §116455 and can be found at

Notification Levels

Title Notification Level (μg/L) Last Updated Edit
1,2,3-Trichloropropane 0.005 Aug 20, 2009
1,2,4-Trimethylbenzene (1,2,4-TMB) 330 May 28, 2001
1,3,5-Trimethylbenzene (1,3,5-TMB) 330 May 24, 2001
1,4-Dioxane 3 May 24, 1998
2-Chlorotoluene 140 Jun 7, 2000
Carbon Disulfide 160 Jul 5, 2001
Chlorate 800 Jan 7, 2002
Methyl Isobutyl Ketone 120 Dec 29, 1999
n-Propylbenzene (isocumene) 260 Oct 27, 2000
Naphthalene 17 Apr 20, 2000
sec-Butylbenzene 260 Oct 27, 2000
tert-Butylbenzene 260 Oct 27, 2000
Tertiary butyl alcohol (TBA) 12 Jun 2, 1999
Vanadium 15 Aug 24, 2000