The colonias of the US-Mexico border are home to hundreds of thousands of people who reside in conditions that would be unacceptable anywhere else in the country. The community health problems of the colonias are many and varied, but environmental contamination ranks among the most pervasive. Contamination of water supplies is an especially significant risk to the health of these communities. The health and environmental problems of colonias are a phenomenon limited to the border region; however, they become problems of national and international importance as the economic development of the border increases as a result of the North American Free Trade Agreement.