Waterborne pathogen monitoring in Jaipur, India reveals potential microbial risks of urban groundwater supply

The Sustainable Development Goals require that 100 mL water samples contain no culturableE. colito classify a water supply as safely managed from a microbial perspective. But small volume sampling is often insufficient for detecting microbial risks. We used culture-based measures of total coliforms andE. colialong with dead-end ultrafiltration (DEUF) and droplet digital PCR (ddPCR) to assess the microbial water quality of an urban water supply in Jaipur, India. Despite the absence of culturableE. coliin 90% of the 100 mL grab samples (n = 20) during the 10-day sampling period, we detected genes associated with protozoan and bacterial pathogens (Giardia,Cryptosporidium, and enterotoxigenicE. coli) in 3 DEUF samples of groundwater (n = 9; volume 59 to 122.4 liters). Of the three groundwater samples positive for waterborne pathogens, two were associated with 100 mL grab samples that were negative for culturableE. coli. Methods with improved analytical sensitivity, such as DEUF and ddPCR, can detect evidence of pathogens in drinking water supplies and supplement conventional culture-based methods to better inform pathogen-specific risk assessment and management.