It is confusing that sometimes when the German sentence is translated into correct English, it is wrong because an unnecessary word is omitted. Then when you translate literally, you are wrong, while the excepted answer is wrong. "The basement is standing under water" is not wrong" nor is "Water is standing in the basement".
I also think that your translations are good. They clearly conjure up the correct images. I don't see why a German idiom must be translated to an English idiom such as "is flooded" which is a moving target depending on what is "flooded". I suspect that translating "The bathroom is flooded" to "Das Bad steht unter Wasser" would be a questionable one.