If you do not get to the water-damaged book quickly there is little you will be able to do. Mold and mildew will set in and ruin the book or the shrinking pages and warped covers will render the book unrecognizable. If the book sports glossy or coated pages they will stick together and it will be beyond the capabilities of even a professional conservator. Before embarking on your home conservation project, make certain you have abundant flat spaces on which to work. As for materials, you will need absorbent paper such as paper towels or blotting paper.
Uninked newsprint is a very absorbent paper.
A fan will be required to circulate cool air and flat heavy weights such as particle board or bricks should be at hand. If the book is sturdy enough, stand it on its edge and fan open the pages. Allow the book to air dry or dry the pages with the fan until they are only slightly damp. Place the paper towels in between groups of pages, about every ten pages. This is known as interweaving.