Impact of pipe material, operation, and disinfectant on cold water plumbing microbiology

Abstract

AbstractThis study examined the effects of pipe materials, pipe diameters, frequency of use, and disinfectant types on the water quality microbiology in experimental pipe rack systems. Two pipe rack systems were installed in buildings in Colorado (CO) and Pennsylvania (PA) and sampled for 8–9 months of operation, respectively, under simulated high and low use conditions. Opportunistic premise plumbing pathogens including Legionella pneumophila, nontuberculous mycobacteria, Pseudomonas aeruginosa, and free‐living amoebae (FLA) were the target organisms. Disinfectant type (free chlorine vs. chloramine) and use frequency (flushed every 12 h vs. weekly) had the greatest impact on bulk water microbiology. Under low use conditions, neither system had detectable disinfectant residual but under high use, residual was detected. Heterotrophic plate count bacteria predominated in the free chlorine system while nontuberculous mycobacteria were predominant in the chloraminated system. P. aeruginosa and FLA were not detected in the free chlorine system and legionellae were not detected in either system.