The five common steps of conventional drinking-water treatment are coagulation, flocculation, sedimentation, filtration and disinfection. Coagulation destabilises fine particles using appropriate chemical addition and mixing. Flocculation uses gentler mixing to form larger, separable flocs. Sedimentation provides controlled conditions for suitable flocs to settle and produces sludge requiring responsible management. Filtration reduces remaining material through selected media or membranes, whose capabilities vary by technology. Disinfection inactivates susceptible microorganisms using appropriate chemical or physical processes and verified operating conditions. UV does not leave a continuing disinfectant residual in downstream distribution. These steps form complementary barriers rather than five interchangeable solutions. Some guides group coagulation and flocculation into one heading and describe four stages instead. The CDC explains the five-step sequence and the importance of selecting treatment for the source water. The Drinking Water Inspectorate emphasises source-specific treatment, a multiple-barrier approach, maintenance and records. Source assessment and representative analysis are needed before equipment selection. Some supplies require additional treatment for dissolved contaminants or saline water. Finished water must also be protected in storage, distribution and building systems. Operational monitoring and appropriate laboratory analysis demonstrate whether the intended treatment is being achieved. Conventional sewage treatment and industrial-system treatment use different frameworks and do not automatically produce potable water. Reviewed 7 October 2026 using CDC and DWI guidance.