Different types of water treatment include physical separation, chemical treatment, biological treatment and disinfection. These overlapping families describe treatment mechanisms, while drinking-water, wastewater and industrial treatment describe applications. Physical processes include screening, sedimentation, flotation and filtration. Coagulation and flocculation can prepare fine particles for separation. Activated carbon adsorbs selected compounds but has finite capacity and is not universal purification. Ion exchange can reduce hardness or selected dissolved ions using appropriate resins and regeneration regimes. Microfiltration and ultrafiltration differ from nanofiltration and reverse osmosis in their capabilities. Reverse osmosis can reduce many dissolved salts but requires suitable pretreatment, concentrate management and verification. Chemical treatment includes oxidation, pH adjustment and corrosion control. Disinfection may use chlorine, UV or ozone, with different operating requirements and limitations. UV does not leave a continuing disinfectant residual. Biological wastewater treatment uses microorganisms in systems such as activated sludge and trickling filters to reduce biodegradable pollution. Conventional sewage treatment does not automatically produce drinking water. Aeration can transfer selected volatile contaminants to air or supply oxygen for biological treatment. Advanced oxidation addresses particular contaminants rather than every possible hazard. Treatment selection needs representative analysis, defined finished-water requirements, complementary barriers, maintenance, monitoring and an agreed failure response. Building-system water hygiene remains an ongoing responsibility. Reviewed 7 October 2026 using EPA, CDC and Drinking Water Inspectorate guidance.