I have cleared all the tiles, repaired all the pipes, but I’m still unable to flood the area. Can anyone help?
You haven't cleared out all the tiles in the areas that need to be flooded....the levers will not operate until all the relevant tiles have been cleared.... refer to the maps contained in the links provided below.
Check out the relevant Wiki page, maps, videos, guides, walkthroughs & hidden gifts/bonuses in these links
You will generally find that the hidden gifts/bonuses are clearly marked on the maps created by Roeland which are contained in these links below