This European Standard applies to drain and sewer systems, which operate essentially under gravity, from the point where the sewage leaves a building or roof drainage system, or enters a road gully, to the point where it is disharged into a treatment or receiving water. Drains and sewers below buildings are included provided that they do not form part of the drainage system of the building. This part covers general matters and sets out definitions of terms that relate to the functional requirements of drain and sewer systems outside buildings.