Examine the book to determine where the text block is separating from the hinge. The easiest way to spot the trouble is to hold the book, spine up, in your hands to see how the pages hang.
Prop the book up. Insert your fingers between the endpaper and spine to pull the two as far apart as possible without separating them further.
Dip the knitting needle in glue or adhesive and insert the needle down the length of the opening. Twirl the needle to ensure the adhesive is evenly distributed. Be careful to use just enough glue or adhesive, as too much can cause the cover and endpaper to feel water damaged.
Insert a piece of wax paper between the cover and endpaper and close the book.
Stack other books, boxes, or any dry, stable item on top of the book to press the cover into place. Leave overnight.
Insert a paper towel sheet every ten pages to soak up water. Change out the sheets every hour. Use care, as wet pages rip easily.
Press the book flat with dry, weighty objects that are impervious to water damage.
Dry the book with a hair dryer once the pages are partially dry and less fragile. Use a low setting. Don’t fan the book out too much, as it can damage the spine. Don’t dry in the sun, as that can fade the print and brown the pages.
Apply acid-free glue to the page by painting a light layer on with a paintbrush or cotton swab.
Dab excess glue with a cotton swab or paper towel.
Place the torn page between sheets of wax paper to prevent glue from sticking pages together.
Press the book for a few hours.