This European Standard specifies requirements for the design of drain and sewer systems outside buildings. It is applicable to drain and sewer systems, which operate essentially under gravity, from the point where the wastewater leaves a building, roof drainage system, or paved area, to a point where it is discharged into a wastewater treatment plant or receiving water body. This document specifies requirements for the hydraulic design of drain and sewer systems and the assessment of the capacity of existing drain and sewer systems.