Floodwater is the water that covers land during a flood — the water itself, not the event. After a river comes over its sides, the floodwater sits in streets and rooms. It is often brown, full of mud and rubbish, and dangerous to walk through. English also likes the plural floodwaters, especially when the water is still spreading or when writers want it to sound huge: The floodwaters rose overnight. Both mean the same kind of water. You would not call tap water floodwater, and you would not call the sea floodwater; it has to be water in the wrong place because of a flood.

洪水（水災時蓋過地面的那些水，多半是髒的）。