AimsTo examine the occurrence and quantity of potential pathogens and an indicator of microbial contamination in the sediments of municipal drinking water storage tanks (MDWSTs), given the absence of such data across the United States. Methods and ResultsSediment samples (87 MDWST) from eighteen locations across ten states of the United States were collected and assayed by qPCR for a range of potential enteric and opportunistic microbial pathogens and a sewage-associated Bacteroides marker. Potential opportunistic pathogens dominated, with the highest detection of occurrence (per cent positive detection; average cell equivalence (CE)) being Mycobacterium spp. (889%; 67 85 x 10(4) CE g(-1)), followed by Legionella spp. (667%; 52 59 x 10(3) CE g(-1)), Pseudomonas aeruginosa (222%; 250 +/- 880CEg(-1)) and Acanthamoeba spp. (389%; 53 +/- 70CEg(-1)), with no detected Naegleria fowleri. Most enteric pathogens (Campylobacter jejuni, Escherichia coli 0157:H7, Salmonella enterica, Cryptosporidium parvum and Giardia duodenalis) were not detected, except foratrace signal for Campylobacter spp. There was significant correlation between theqPCR signals of Legionella spp. and Acanthamoeba spp. (R-2=061, n=87, P=00001). Diverse Legionella spp. including Leg.pneumophila, Leg.pneumophila sg1 and Leg.anisa were identified, each of which might cause legionellosis. ConclusionsThese results imply that potential opportunistic pathogens are common within MDWST sediments and could act as a source of microbial contamination, but need downstream growth to be of potential concern. Significance and Impact of the StudyThe results imply that opportunistic pathogen risks may need to be managed by regular tank cleaning or other management practices.