Of course water and severe damp can leave a nasty edge called a "tidemark" this can be just as difficult to remove especially if the book is rare and has the provenance of being written on by someone famous (tut tut) the writing medium would need to be "fixed" to the paper before the operation can commence.
Strange how sometimes just one page in the whole book can get damaged
by water, but it does happen especially with old cookery books, the
pages in these get subjected to a whole range of different stains,
including booksellers rubber ink stamps!
Next Page Removing Ink Stains