Chlorine dioxide (ClO₂) has emerged as a widely used disinfectant in water treatment due to its broad-spectrum antimicrobial efficacy and reduced formation of halogenated disinfection by-products compared with conventional chlorination. Despite its increasing adoption, the environmental sustainability of different ClO₂ production routes remains insufficiently quantified. Most previous life cycle assessment (LCA) studies treat chlorine dioxide generation as a single aggregated process, without distinguishing among alternative synthesis pathways. This study addresses this gap through a comparative LCA of ten industrial ClO₂ production methods. An attributional LCA framework was applied using inventory data from the ecoinvent v3.8 database. Environmental impacts were evaluated across six categories—Global Warming Potential, freshwater ecotoxicity, human toxicity, water consumption, acidification, and eutrophication—using the EF 3.0, TRACI 2.1, and USEtox impact assessment methods. The functional unit was defined as 1 kg of ClO₂ produced under cradle-to-gate system boundaries. Sensitivity analyses were conducted to address sodium chlorite proxy assumptions, electricity grid carbon intensity, and co-product allocation scenarios. Results indicate substantial variation in environmental performance across production routes. Global Warming Potential ranged from 3.86 to 5.20 kg CO₂-eq per kg ClO₂, representing a 35% difference between the lowest and highest impact methods. Electrochemical production and the Cl₂ + NaClO₂ route exhibited the lowest overall climate impacts, whereas hydrochloric-acid-based methods showed higher toxicity indicators. Contribution analysis revealed that precursor production dominates environmental burdens, accounting for 85–97% of total GWP. Sensitivity analysis identified a critical electricity carbon-intensity threshold of approximately 0.35 kg CO₂ kWh⁻¹, below which electrochemical production becomes environmentally advantageous. These findings demonstrate that environmental performance varies significantly across synthesis routes and that electrochemical chlorine dioxide production represents a conditionally sustainable option depending on regional energy infrastructure. The results provide quantitative benchmarks to support technology selection by water utilities and regulators.