Premise Plumbing “CT” (PPCT) as a Control Parameter for Opportunistic Pathogens

High Resolution Image Download MS PowerPoint Slide The product of disinfectant concentration and time (CT) is widely applied as a key pathogen inactivation parameter during potable water treatment. Here, we introduce the concept of premise plumbing CT (PPCT) as a part of an integrated framework for the control of opportunistic pathogens (OPs), such as Legionella pneumophila and Mycobacterium avium . A method is proposed for calculating CT at a given location in premise plumbing during stagnation events and demonstrated at scale in a chloraminated premise plumbing rig. Chloramine decay rates in stagnant PEX pipes were 2–3 orders of magnitude greater than in glass jars and dependent on initial chloramine concentration, contact time, temperature, pipe diameter, and flow rate. PPCT varied from 0 to 408 mg min/L from one pipe segment to another. No culturable L. pneumophila was detected in the test system pipes with PPCT > 78 mg min/L, which is comparable to reported CT thresholds for biofilm-associated L. pneumophila inactivation. Extending the concept to a lab-operated water heater yielded an estimated PPCT of 342.9 mg min/L, but robust growth of M. avium occurred in the tank up to 4 log CFU/mL, indicating extreme chloramine resistance. The PPCT framework introduced herein could provide a fundamental benchmark to help control OPs in the premise plumbing.