Impacts of organic matter migrating from pipe materials on microbial regrowth in drinking water

Polymeric materials are widely used in premise plumbing. To assess the potential of pipe materials to promote microbial regrowth in drinking water, we incubated drinking water in a new cross-linked polyethylene pipe (N-PEX), a new steel pipe lined with powdered polyethylene (N-SPE), and an old steel pipe lined with powdered polyethylene (O-SPE). As a reference, we also incubated drinking water in a carbon-free glass bottle (REF). Free chlorine rapidly depleted to below the quantification limit in the pipe incubations. While the original drinking water contained 0.4 mg C/L of dissolved organic carbon (DOC), the DOC concentration in N-PEX, N-SPE and O-SPE increased to 5.2, 3.1 and 1.7 mg C/L, respectively, after 8 days of incubation. The total cell count (TCC) in N-PEX, N-SPE, and O-SPE increased from <10³ cells/mL to 6.0 × 10⁵, 2.8 × 10⁵, and 3.6 × 10⁶ cells/mL after 8 days of incubation, respectively. On the other hand, the TCC in REF increased to 1.4 × 10⁵ cells/mL after 14 days of incubation. Dominant bacterial groups were different under the different incubation conditions. These results indicated that organic matter migrating from pipe materials promote microbial regrowth and affect the microbial community composition in drinking water.