Water quality controls on toxic DBPs: A global multivariate assessment of THMs, HAAs, and HANs

This study provides the first global statistical assessment of how water quality parameters (WQPs) influence the formation and regulatory exceedances of major disinfection by‑products (DBPs) in drinking water (disinfected tap water), including trihalomethanes (THMs), haloacetic acids (HAAs), and haloacetonitriles (HANs). A dataset of over 800 drinking water samples from 30 countries was analysed using multivariate techniques (PCA, CCA, MRA, FAMD) to disentangle the contributions of seven WQPs to DBP formation. Bromide emerged as the dominant driver of DBP speciation, with the Br⁻:Cl⁻ ratio strongly favouring brominated DBPs, while temperature showed consistent positive associations with multiple DBPs. TOC, pH, and inorganic nitrogen species exhibited compound‑specific associations, reflecting the diverse precursor and formation pathways across DBP classes. Globally, HAAs were the most prevalent DBP group and exceeded safety thresholds more frequently than THMs and HANs. Elevated THMs and HANs levels occur in several European countries (France and Croatia, respectively) dependent on source waters chemistry, such as high Br⁻ levels. Iran from Middle East and India report the highest HAAs occurrence, driven by regional reliance on unregulated or saline sources. Overall, DBP occurrence was more strongly governed by water‑matrix chemistry than by geographic location or treatment type, underscoring the need for locally tailored water‑treatment strategies that account for parameters such as bromide levels, NOM characteristics, and temperature‑driven variability to effectively control DBP formation and ensure safe drinking water. This work offers practical guidance for water utilities and regulatory agencies by clarifying how fluctuations in WQPs shape DBP formation under typical operational conditions.