From the State Department FAQ's, sounds like you have to reapply, not just renew (though of course it depends on the exact damage, though they do mention water damage)
a:If your passport has been significantly damaged, especially the book cover or the page displaying your personal data and photo, you will need to apply for a new passport. You will need to submit the following in person (See Where to Apply):
The damaged passport
Form DS-11
All documents required by Form DS-11, including citizenship documentation (i.e. birth certificate)
Water damage, a significant tear, unofficial markings on the data page, missing visa pages (torn out), a hole punch and other injuries may constitute “damage” requiring use of Form DS-11.
Normal wear of a U.S. passport is understandable and likely does not constitute “damage”. For instance, the expected bend of a passport after being carried in your back pocket or fanning of the visa pages after extensive opening and closing. In most cases of normal wear, you may renew your passport by mail using Form DS-82.
Please remember, if you try to renew a significantly damaged passport using Form DS-82, you may be asked by the Passport Agency to apply again using Form DS-11 and incur additional fees.