A passive overflow well is used in drainage system networks to intercept and trap initial rainwater and dry-weather flow sewage, achieving source control by diverting and reducing direct discharge of polluted water. This helps prevent downstream water bodies from becoming foul-smelling. When used in conjunction with storage reservoirs, it can divert the dirtiest wastewater to the reservoir at the source, allowing cleaner rainwater to be discharged directly into natural water bodies, thereby reducing the burden on sewage treatment plants.