All sewers and side effluents that were declared prior to 1 all are part of the public wastewater system owned by Thames Water and managed by Thames Water. There are different applications for different sizes of sewers. Class 1 1 160 mm in diameter or smaller (domestic/commercial) Class 2 160 – 375 mm in diameter Class 3 more than 375 mm Diameter For all classes, with the exception of Class 1 on the national territory, we must carry out, before the start of the work, a surveillance examination for the closed circuit (CCTV) to determine if repair work is necessary. Further examination is needed when your building is completed to verify that the sewers have not been damaged. If you have not obtained our consent, we may, in certain circumstances, require that you stop your work and that the buildings built above the public sewers be eventually demolished.