There are approximately 160,000 public drinking water utilities and more than 16,000 wastewater utilities in the United States. About 84 percent of the U.S. population receives its potable water from these drinking water utilities and more than 75 percent has its sanitary sewage treated by these wastewater utilities. The drinking water and wastewater sector (Water Sector) is vulnerable to a variety of attacks, including contamination with deadly agents and physical and cyber attacks. If these attacks were to occur, the result could be large numbers of illnesses or casualties or denial of service that would also affect public health and economic vitality. Critical services such as firefighting and health care (hospitals), and other dependent and interdependent sectors such as energy, transportation, and food and agriculture, would suffer negative impacts from a denial of Water Sector service. (DHS & EPA, Water Critical Infrastructure and Key Resources Sector Specific Plan as input to the National Infrastructure Protection Plan, May 2007)