Beyond the Bulk: Fraction-Specific Total Organic Carbon Profiling for Proactive Water Quality Management

Abstract Total organic carbon (TOC) is widely used to monitor water quality, but its value as a single metric is increasingly limited in water management. Bulk TOC does not distinguish organic fractions with different reactivities and associated risks, limiting its ability to predict disinfection byproduct (DBP) formation, microbial regrowth, and biofouling. Fraction-based characterization addresses these limitations by resolving bulk TOC into operationally defined fractions, transforming a conventional compliance water-quality metric into a more precise diagnostic tool. This review critically synthesizes current knowledge on TOC profiling and its implications for water treatment, evaluating fractionation methods, source water variability, and the roles of organic fractions in DBP formation and biofouling. The synthesis demonstrates that water quality risks are governed not only by the TOC concentration but also by the distribution and transformation of specific fractions throughout treatment systems. Hydrophobic and aromatic fractions dominate DBP precursors, while low-molecular-weight fractions are key drivers of microbial regrowth and biofouling. Finally, this review identifies knowledge gaps and opportunities to advance the TOC profile as a process-optimizing tool for water quality management by integrating surrogate indicators for practical application in full-scale water systems.