Seven widely used methods of water treatment are coagulation and flocculation, sedimentation, granular-media filtration, activated-carbon adsorption, ion exchange, membrane separation and disinfection. There is no universal official list of exactly seven methods: this guide groups related operations and distinguishes technologies with different functions. Coagulation and flocculation form removable particle aggregates, sedimentation separates suitable solids by gravity, and granular filtration captures remaining particles. Activated carbon adsorbs selected dissolved compounds, ion exchange changes dissolved-ion composition, and membrane processes include reverse osmosis for dissolved-solids removal. Disinfection inactivates microorganisms under validated conditions. These methods are not compulsory stages for every supply. Treatment selection depends on representative source-water analysis, intended use, operating conditions and finished-water requirements. DWI guidance supports a multiple-barrier approach, competent maintenance and monitoring. The full article draws on DWI, CDC and EPA guidance, explains limitations and waste streams, and includes links to related process and chlorination articles. Reviewed 7 October 2026.