This European Standard is applicable to the investigation and assessment 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 sewage leaves a building or roof drainage system, or enters a road gully, to the point where it is discharged into a treatment works 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 of this European Standard specifies general requirements for the investigation and assessment of drain and sewer systems outside buildings.