On January 21, 2001, a two-sentence letter was discovered in a New York apartment threatening to poison the water systems of 28 major U.S. cities, including New York. The letter had been prepared by someone with ties to Al-Qaeda, a shadowy group of Islamic extremists largely unknown to a nation preoccupied with other matters. The events that unfolded relating to this letter served to highlight the vulnerability of the nation’s water supply, accentuate the need for a threat assessment and warning matrix within the water industry, illustrate the need for relationships to share and manage information by and between law enforcement agencies and within the water industry, and demonstrate the political exposure associated with the failure to share information in a timely manner. Threats to attack or, more commonly, contaminate, water systems are not unusual. There are hundreds of threats against municipal water systems each year ~Fig. 1!. Estimates of water threats vary widely. This is due in part to the lack of a comprehensive reporting mechanism, failure to recognize incidents as malicious, the tendency for utilities to dismiss incidents as ‘‘vandalism,’’ a lack of interest from academia, and a general lack of interest from law enforcement agencies. Water managers are very familiar with the ‘‘natural’’ threats from bacteria, viruses, protozoa, coliforms, and algaes; they are generally less familiar with the threat from criminals and terrorists. Movies, television, and novels often depict water supplies as ‘‘the ultimate terrorist target.’’ Raw water supplies, wells, reservoirs, dams, intake structures, treatment plants, finished water reservoirs, tanks, water towers, and even distribution systems represent vast and almost indefensible targets. Terrorism in the new millennium is complicated by the range of potential attackers, the array of weapons available to them, and their ruthless creativity. Technology, particularly the internet, has eliminated many of the engineering barriers that historically have helped to limit the effectiveness of attacks. Weapons that were once the province of nations now exist in the hands of individual terrorists. Chemical, biological, and potentially even nuclear weapons in the hands of someone bent on creating death, destruction, or fear are indeed daunting concepts, particularly for the local utility operator whose greatest concern has traditionally been taste, odor, or system pressure. Special Agent William Zinnikas responded to the Queens apartment to investigate the threat and recover the letter. He faxed a copy to FBI headquarters where, pursuant to FBI protocol, the letter was evaluated for credibility using the FBI matrix of behavioral resolve, technical capacity, and potential effectiveness. ‘‘The letter itself offered no specific threat, but because there were two columns of cities listed, we forwarded it to headquarters for further analysis’’ ~Zinnikas 2001!. The analysis determined that the threat was not credible and that, had the information remained within the FBI, the matter would have been listed as another