Disinfection Byproducts in Direct Potable Reuse and Conventional Drinking Waters: Influence of pH, Cu²⁺, and Water Age under Distribution System and Premise Plumbing Conditions

Disinfection byproduct (DBP) formation and transformation in distribution and premise plumbing systems are incompletely characterized, especially in wastewater-impacted waters. We evaluated the impact of pH, Cu²⁺ addition, and water age on 54 regulated and unregulated DBPs after chlorination of direct potable reuse (DPR) and conventional drinking waters. DPR water produced 1.6× higher DBP and 3.9× higher calculated additive toxicity (CAT) yields than conventional drinking water. Iodinated trihalomethanes (I-THMs) reached 63 μg/L in DPR and 25 μg/L in conventional drinking water. Raising pH to 10 increased trihalomethanes, I-THMs, and dihalogenated haloacetamides but decreased haloacetaldehydes. CAT values decreased with increasing pH, primarily due to base-catalyzed degradation of more toxic DBPs. Cu²⁺ addition had minimal impact on DBP formation and speciation, except for hindering I-THM formation in both waters and catalyzing trichloroacetaldehyde formation in the conventional drinking water. DBP levels increased over time at pH 7-8 but not at pH 10. CAT declined at pH 7 and remained stable at pH 8-10, indicating that higher water age does not necessarily increase DBP risk. CAT results have the caveat that they are inherently relative; they are intended for comparative purposes between water types and conditions rather than as an absolute measure of risk.