**Interactive E**ff**ects of Copper Pipe, Stagnation, Corrosion Control, and Disinfectant Residual Influenced Reduction of** *Legionella pneumophila* **during Simulations of the Flint Water Crisis**

#### **Rebekah L. Martin 1,2, Owen R. Strom 3, Amy Pruden 1 and Marc A. Edwards 1,\***


Received: 29 July 2020; Accepted: 31 August 2020; Published: 4 September 2020

**Abstract:** Flint, MI experienced two outbreaks of Legionnaires' Disease (LD) during the summers of 2014 and 2015, coinciding with use of Flint River as a drinking water source without corrosion control. Using simulated distribution systems (SDSs) followed by stagnant simulated premise (i.e., building) plumbing reactors (SPPRs) containing cross-linked polyethylene (PEX) or copper pipe, we reproduced trends in water chemistry and *Legionella* proliferation observed in the field when Flint River versus Detroit water were used before, during, and after the outbreak. Specifically, due to high chlorine demand in the SDSs, SPPRs with treated Flint River water were chlorine deficient and had elevated *L. pneumophila* numbers in the PEX condition. SPPRs with Detroit water, which had lower chlorine demand and higher residual chlorine, lost all culturable *L. pneumophila* within two months. *L. pneumophila* also diminished more rapidly with time in Flint River SPPRs with copper pipe, presumably due to the bacteriostatic properties of elevated copper concentrations caused by lack of corrosion control and stagnation. This study confirms hypothesized mechanisms by which the switch in water chemistry, pipe materials, and different flow patterns in Flint premise plumbing may have contributed to observed LD outbreak patterns.

**Keywords:** flint; *Legionella pneumophila*; copper; PEX; iron; chlorine; premise plumbing
