Drinking water microbiology in a water-efficient building: stagnation, seasonality, and physicochemical effects on opportunistic pathogen and total bacteria proliferation

Christian J. Ley; Caitlin R. Proctor; Gulshan Singh; Kyungyeon Ra; Yoorae Noh; Tolulope Odimayomi; Maryam Salehi; Ryan Julien; Jade Mitchell; A. Pouyan Nejadhashemi; Andrew J. Whelton; Tiong Gim Aw

doi:10.1039/D0EW00334D

Drinking water microbiology in a water-efficient building: stagnation, seasonality, and physicochemical effects on opportunistic pathogen and total bacteria proliferation†

Christian J. Ley,

^a Caitlin R. Proctor,^abcd Gulshan Singh,^e Kyungyeon Ra,^b Yoorae Noh,^b Tolulope Odimayomi,^a Maryam Salehi,^f Ryan Julien,^g Jade Mitchell,^g A. Pouyan Nejadhashemi,^g Andrew J. Whelton

^ab and Tiong Gim Aw

*^e

Author affiliations

* Corresponding authors

^a Environmental and Ecological Engineering, Purdue University, West Lafayette, IN 47907, USA

^b Lyles School of Civil Engineering, Purdue University, West Lafayette, IN 47907, USA

^c Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47906, USA

^d School of Materials Engineering, Purdue University, West Lafayette, IN 47907, USA

^e Department of Environmental Health Sciences, School of Public Health and Tropical Medicine, Tulane University, 1440 Canal Street, Suite 2100, New Orleans, LA 70112, USA
E-mail: taw@tulane.edu
Tel: +1 504 988 9926

^f Department of Civil Engineering, University of Memphis, Memphis, TN 38152, USA

^g Department of Biosystems Engineering, Michigan State University, East Lansing, MI 48824, USA

Abstract

The rising trend in water conservation awareness has given rise to the use of water-efficient appliances and fixtures for residential potable water systems. This study characterized the microbial dynamics at a water-efficient residential building over the course of one year (58 sampling events) and examined the effects of water stagnation, season, and changes in physicochemical properties on the occurrence of opportunistic pathogen markers. Mean heterotrophic plate counts (HPC) were typically lowest upon entering the building at the service line, but increased by several orders of magnitude at the furthest location in the building plumbing. Legionella spp. and Mycobacterium spp. were detected in the plumbing, with the highest detection occurring in the summer months. Log-transformed HPC were significantly correlated with total cell counts (TCC) (r_s = 0.714, p < 0.01), Legionella spp. (r_s = 0.534, p < 0.01), and Mycobacterium spp. occurrence (r_s = 0.458, p < 0.01). Reduced water usage induced longer stagnation times and longer stagnation times were weakly correlated with an increase in Legionella spp. (r_s = 0.356, p < 0.001), Mycobacterium spp. (r_s = 0.287, p < 0.001), TCC (r_s = 0.216, p < 0.001) and HPC (r_s = 0.395, p < 0.001). Interrelationships between seasonal shifts in water chemistry and genus-level genetic markers for opportunistic pathogens were revealed. This study highlights how drinking water microbiology varies seasonally and spatially throughout a low-flow plumbing building and highlights the possible unintended consequences associated with reduced water usage and increases in stagnation.

Environmental Science: Water Research & Technology

Drinking water microbiology in a water-efficient building: stagnation, seasonality, and physicochemical effects on opportunistic pathogen and total bacteria proliferation†

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