Determine the type of book you're dealing with. Books that have glossy pages or specialty coatings can only be restored by a professional. The best odds of successful restoration lie with hard cover books and standard paper. Also, if the book is easily replaceable, it may not be worth your time and effort to attempt restoration.
Determine the extent of the water damage. If the book has been floating in water for days, it is likely that that glue in the binding has loosened and this reduces the chances for successful restoration. If the book has already started to grow mold, it should not be restored at home. If it is irreplaceable, a professional may attempt the restoration. On the other hand, if the book has been recently soaked and you have recovered it from the water quickly, you have an excellent chance at drying the book out successfully.
Insert paper towels into the book about every ten or so pages. Lay a single layer of paper towel to cover the entire page. Use a premium brand of paper towel known for its absorption. Be very gentle when opening the wet book and turning soaked pages as they will easily tear. Close the book on the paper towels carefully.
Pull open a baby diaper and wrap around the outside of the book. Baby diapers are incredibly absorbent and will wick out moisture in the cover of the book better than a paper towel. The inside of the diaper should touch the book's cover.
Lay board over top of book and weigh it down with bricks or cans. To help absorption of the water, the book needs pressure applied to it. Center the board over the front face of the diaper-wrapped book and place bricks or cans on the board to weigh it down. Remove the board and change the paper towels for fresh ones every two hours, replacing the board when you're done.
Stand the book upright in front of the fan to finish drying. When the book's pages are only slightly damp to the touch, remove the paper towels and diaper. Stand the book up on its end with the pages fanned open in front of a fan. Check book every two hours to test dryness. When pages feel dry to the touch, turn off the fan but leave the book upright for a few days to ensure that the spine is dry.