Reference pathogen numbers in urban stormwater for drinking water risk assessment

Targeted stormwater event-based monitoring of adenovirus, Cryptosporidium and Campylobacter , the human health reference pathogens of viruses, protozoa and bacteria, respectively, was undertaken to determine numbers prior to water recycling via an aquifer. This allowed the determination of a 95th percentile of reference pathogen numbers in stormwater (2 n/L for adenoviruses, 1.4 n/L for Cryptosporidium and 11 n/L for Campylobacter ) and was used in a quantitative microbial risk assessment to determine the required microbial inactivation targets. Log10 removals through treatments and/or control measures to manage pathogen risks were determined for different end uses based on the 95th percentile numbers. Public open space irrigation was found to require 1.6 log10 reduction for viruses, 0.6 log10 for protozoa and 1.2 log10 for bacteria; third pipe systems which include potential exposure through toilet flushing and washing machine use require 2.7 log10 reduction for viruses, 1.8 log10 for protozoa and 2.3 log10 for bacteria; and drinking water requires 5.8 log10 reduction for viruses, 4.8 log10 for protozoa and 5.3 log10 for bacteria. These results are the first reported for an Australian urban stormwater site with sufficient data for a drinking water risk assessment.