The events of September 11 brought a new reality to the water world. Since California was the destination of the four hijacked planes, security was immediately tightened at dams, aqueducts and water treatment plants. This issue of Western Water examines the issue of water security and the preparedness of federal, state and local agencies to the threat of terrorism. In addition to physical security and bioterrorism, it focuses on the type of long-term security measures being implemented to ensure a safe water supply. While certainly not the last word on the issue, this article will provide a glimpse into a world that was transformed forever September 11.