If you have weeks before it is do, just rewrite it. Even if it is super long, copying it shouldn't take more than an hour at most. You should still be able to read what it says. If it was written on a specific paper that your teacher gave you, just tell her your cat knocked a cup of water on it and you need a second copy.
If you did it on computer, just reprint it. If it was done long hand rewrite it. Teacher will be mad if you turn it in al wet and runny.
write it again
your report was in pencil and paper? Most students use computers if the paper is ruined by water you just print out another copy. Take what you have and turn it in.. usually when water is spilled on paper it runs off use an iron to press out wrinkles and dry it. Done it before in the olden days when there was no printers!