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

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.