Surface water, particularly that found in urban streams, is often contaminated by both chemicals and pathogens, disease-causing organisms such as bacteria, which can cause illnesses even at low concentrations. Potential pathogen sources include septic tanks, public wastewater treatment plant effluent, and leaking sewage collection systems. Groundwater is also vulnerable to pathogens from surface sources where rapid infiltration or limited filtration capacity occurs. However, the extent of pathogens in groun