Asellus aquaticus as a potential carrier of Escherichia coli and other coliform bacteria into drinking water distribution systems

Individuals of the water louse, Asellus aquaticus, enter drinking water distribution systems in temperate parts of the world, where they establish breeding populations. Populations of A. aquaticus in surface water from 2 ponds were analysed for associated faecal indicator bacteria and the risk of A. aquaticus transporting bacteria into distribution systems was assessed. Concn. of ≤2 Escherichia coli and 5 total coliforms ml-1 were measured in the water and 200 E. coli and >240 total coliforms ml-1 in the sediments of the investigated ponds. Concn. of A. aquaticus associated bacteria never exceeded 3 E. coli and 6 total coliforms A. aquaticus-1. During exposure to high concn. of coliforms, concn. reached 350 coliforms A. aquaticus-1. A. aquaticus associated E. coli were only detected as long as E. coli were present in the water and sediment. The calculated probability of exceeding drinking water guideline values in non-disinfected systems by intrusion of A. aquaticus was low. Only in scenarios with narrow pipes and low flows, did total coliforms exceed guideline values, implying that the probability of detection by routine monitoring is also low. The study may expand the knowledge base for evaluating incidents with the presence of coliform indicators in drinking water by showing that intruding A. aquaticus are not important carriers of E. coli or other coliform bacteria even when emerging from faecally contaminated waters.