3, same answer as above. The water can’t be used if it was recooked on Shabbos.
4, only something that’s completely dry can be reheated on Shabbos. Once liquid is involved, you can’t reheat it on Shabbos.
The concept that “it’s impossible to cook something that’s already cooked” (which allows for reheating completely dry cooked Foods) only applies to something that’s completely dry.
As always, confirm with a LOR