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 culturable E. coli to 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 and E. coli along 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 culturable E. coli in 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 enterotoxigenic E. 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 culturable E. 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. [ABSTRACT FROM AUTHOR]