Terrorists take action against innocent people to kill, create fear and to destroy confidence.  Al Qaeda has explored many ways to hit the U.S. and US interests.  Water contamination is included in their plan.

“In one of the more brazen plots since September 11, investigators discovered that terrorists had cut holes in a tunnel beneath the U.S. embassy in Rome and planned to poison the water supply with cyanide.”

The National Review Online, October 16th, 2003

“Al Qaeda Warns of Threat to Water Supply”
A spokesman for al Qaeda has told an Arabic-language news magazine that the terror group will try to use poisons to attack the United States, specifically threatening to contaminate the nation’s water supply.

Abu Mohammed al-Ablaj told the London-based al-Majallah magazine that “al Qaeda [does not rule out] using sarin gas and poisoning drinking water in U.S. and Western cities”

Washington Times May 23, 2003. (washingtontimes.com)

Additionally there have been theft of utility maps of water distribution lines and break-ins to water utility plants have been reported..