Molecular analysis of point-of-use municipal drinking water microbiology Eric P. Holinger a , Kimberly A. Ross a , Charles E. Robertson a , Mark J. Stevens b , J. Kirk Harris b , Norman R. Pace a, * a Dept. of Molecular, Cellular, and Developmental Biology, University of Colorado, CB 347, Boulder, CO 80309-0347, USA b Dept. of Pediatrics, University of Colorado School of Medicine, Aurora, CO 80045, USA article info Article history: Received 29 August 2013 Received in revised form 13 November 2013 Accepted 15 November 2013 Available online 27 November 2013 Keywords: Drinking water bacteria Drinking water distribution systems Ribosomal RNA sequences Pyrosequences Opportunistic pathogens abstract Little is known about the nature of the microbiology in tap waters delivered to consumers via public drinking water distribution systems (DWDSs). In order to establish a broader understanding of the microbial complexity of public drinking waters we sampled tap water from seventeen different cities between the headwaters of the Arkansas River and the mouth of the Mississippi River and determined the bacterial compositions by pyrose- quencing small subunit rRNA genes. Nearly 98% of sequences observed among all systems fell into only 5 phyla: Proteobacteria (35%), Cyanobacteria (29%, including chloroplasts), Actinobacteria (24%, of which 85% were Mycobacterium spp.), Firmicutes (6%), and Bacter- oidetes (3.4%). The genus Mycobacterium was the most abundant taxon in the dataset, detected in 56 of 63 samples (16 of 17 cities). Among the more rare phylotypes, considerable variation was observed between systems, and was sometimes associated with the type of source water, the type of disinfectant, or the concentration of the environmental pollutant nitrate. Abundant taxa (excepting Cyanobacteria and chloroplasts) were generally similar from system to system, however, regardless of source water type or local land use. The observed similarity among the abundant taxa between systems may be a consequence of the selective influence of chlorine-based disinfection and the common local environments of DWDS and premise plumbing pipes. ª 2013 Elsevier Ltd. All rights reserved. 1. Introduction Federal US guidelines regulate the chemical and microbio- logical quality of treated drinking water as it leaves water treatment plants, but only highly specific monitoring, for fecal indicator bacteria, is required for water in the distribution system pipes (US 40 CFR Part 141: http://cfr.regstoday.com/ 40cfr141.aspx). Beyond the absence of indicators, little is known about the microbiology that is dispensed from point- of-use taps in water distribution systems, and there are no consistent regulatory standards for microbiological quality once the water passes the meter at a private residence or business establishment. Biofilms are known to be ubiquitous within DWDS and premise plumbing (Deines et al., 2010; Simoes et al., 2006; Yu et al., 2010), and can influence the * Corresponding author. Tel.: þ1 303 735 1864; fax: þ1 303 492 7744. E-mail addresses: norman.pace@colorado.edu, nrpace@colorado.edu (N.R. Pace). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/watres water research 49 (2014) 225 e235 0043-1354/$ e see front matter ª 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.watres.2013.11.027