The terrorist attacks of 9/11/2001 resulted in an evaluation of security risks in the many infrastructures that our Nation's health and well being depend upon, including contamination of public water supplies. A municipal drinking water system can be contaminated either intentionally or accidentally. Historical evidence suggests that threats of intentional contamination are probable, and in fact, do occur. In the event of an actual or suspected case of contamination, whatever the cause, a critical first step is the identification and analytical confirmation of the contaminant. To help meet this need, a new tool is being developed, namely a compendium of analytical methods for chemical, biological, and radiological (CBR) contaminants that could pose a threat to public water supplies. Called NEMI-CBR, it is a derivative of the National Environmental Methods Index (NEMI), a freely accessible database of environmental methods searchable on the Internet at http://www.nemi.gov. A companion expert system, the CBR Methods Advisor, can be used to quickly guide a user to the best method for a given situation in which limited information is available regarding the possible identity of an intentional contaminant. These new software tools designed to help safeguard public water supplies are described in this paper. Includes 6 references, figures.