I received a book recently (I've just finished reading it in fact) and I didn't really notice this until I started reading it, but there are about 50 pages that are all wavy. They are perfectly readable, just wavy. I know from a stamp in the back cover that this was a book taken out of circulation at a library and it has been well-read--lots of creases in the spine. My question is, is that waviness in the pages water damage?

I've already decided to consider this an unpostable book and offer it for free with a particular type of order but I truly don't know what water damage looks like in a book and I want to have an idea if I run across books with it.

It could be.  Usually if you look carefully at the pages, you can see the stain line between what was wet and was wasn't wet.  Water damage can be pretty hard to spot though.  Wavy pages are a good sign of it.

wavy pages could also be an indication of high humidity where the book was kept.

My personal experience with water damage is that if it covers 50 pages, it would have been pretty obvious at the time it was received, unless you literally did not look at the book when it arrived. 

Well I've had brand new books w/wavy pages fresh from the store. Cheap paper.  I would guess since this is a former library book and probably read lots of times that it's water damage.  Usually there will be a water mark of some kind on the page if water was spilled onto it but not necessarily with humidity damage.

Wavy pages don't always mean water damage.( IMO ). I have bought a couple of new books that the pages look wavy . I think  they are cutting cost and using cheaper paper or something. I have some books that are over 40 years old and they look better than some of the newer books I've gotten the last few years.

Usually with water damage, the damaged pages will feel a little different, as well.  A little rougher or thicker.

Books with pages wavey from humidity usually have more uniform waves, and all or most pages are affected.  With only 50 pages, it's probably water damage. 

I had a similiar question...this post has helped me alot.  I received a book today that I felt had had water damage...a couple pages look like they have watermarks but, at least 1/2 the book has wavy pages and the paper feels and looks different...like maybe it is a bit more brittle?!  The book feels thicker and heavier than it should (compared to its sequel of the same number pages) and when you fan the pages it doesn't have that whisper-like sound rather it sounds cracky and almost like the book groans...

Christy - yours definitely sounds like water damage. Thicker, crackly/brittle pages are almost always the clencher for water damage.

Thank you everyone for the information. I still can't decide if it's water damage or not, but I'll put it  out as an unpostable and ask if anyone wants it along with another couple of books I'm going to put in a deal at some point. It's certainly readable, but you can tell it was well-loved by the patrons at the library--it was read a lot if I go by the creases in the spine!

I too have seen books recently that are wavy... but when I look closely at them.. I can't see any water staining and pages are not brittle and crackely.   In fact, I often pull them back to look at them and STILL can't be for sure if it was water damage.  I generally put them on my freebie list just to be on the safe side, but I don't ding the sender unless the damage is clearly water.