Septic tanks, sewage effluents, and landfills can release microbial pathogens into groundwater. This problem is amplified in the so-called colonias along the U.S.-Mexico border and other low-income areas around the world that have no public sewage systems. The result is often outbreaks of groundwater-associated disease for which enteric viruses and bacteria, spread via a fecal-oral route, are responsible. However, due to difficulties and limitations in detection and surveillance of disease outbreaks, the causative agents for more than 50% of the outbreaks are unknown, though the clinical features suggest a viral etiology for most of those cases [U.S. Centers for Disease Control and Prevention, 1993]. Enteric pathogens such as E coli 0157:H7, Campylobacter, Enteroviruses, Hepatitis A virus, and caliciviruses have been responsible for groundwater-related microbial infections in humans. Inexpensive solutions to this problem are urgently needed. The recent threat of bio-terrorism and concerns about the safety of drinking water supplies further add to that urgency.