Purpose of Review <p>Far-UVC irradiation at 222&#xa0;nm (UV₂₂₂), typically emitted by krypton chloride excimer lamps, has emerged as a promising mercury-free platform for water treatment. This review evaluates recent progress in UV₂₂₂-based water treatment, with conventional 254&#xa0;nm UV irradiation (UV₂₅₄) as the primary benchmark, focusing on disinfection, micropollutant degradation, and UV₂₂₂-induced dissolved organic matter (DOM) transformation in relation to post-chlorination disinfection byproduct (DBP) formation.</p> Recent Findings <p>UV₂₂₂ shows strong disinfection performance against representative bacteria and viruses, although its relative advantage over UV₂₅₄ is more variable for fungal spores. For micropollutants, compiled paired photolysis data indicate that UV₂₂₂ generally accelerates direct photolysis relative to UV₂₅₄, with the enhancement arising from stronger absorptivity, higher quantum yield, or both depending on compound structure. UV₂₂₂-based advanced processes further broaden the treatment scope beyond direct photolysis through reactive-species-mediated transformation. However, UV₂₂₂ can also reshape DOM composition and DBP precursor pools. Sole UV₂₂₂ may reshape DOM molecular composition without large DBP increases, whereas nitrate-containing systems can selectively amplify halonitromethane formation.</p> Summary <p>UV₂₂₂ should not be viewed simply as a more reactive substitute for UV₂₅₄. Its practical value depends on balancing disinfection and contaminant-removal benefits against matrix-dependent DOM transformation and downstream DBP risks. Future studies should focus on DOM molecular transformation and DBP precursor restructuring, particularly the role of nitrogen incorporation in linking these two processes, as well as realistic treatment-train evaluations.</p>