O-Phthalaldehyde (OPA) is a high-level disinfectant and non-oxidizing biocide widely used in healthcare and industrial water treatment. It provides rapid and broad-spectrum activity against bacteria, fungi, viruses, and mycobacteria. OPA is commonly applied for disinfection of endoscopes, dialysis equipment, and hospital water systems, as well as in industrial circulation water, pharmaceutical facilities, and laboratory diagnostics. With strong efficacy, low corrosion risk, and excellent material compatibility, OPA ensures safe and reliable microbial control across critical applications.