Water damage is one of the most common types of damage to tapes in the event of a major 'incident' involving them. This can result from anything from a broken pipe or a flood to a fire. In any event, there are several things you should -- and should not -- do when dealing with a soaked tape.
The first thing you need to do is to dry the tape out quickly -- but not too quickly. While damage is likely to increase if the tape sits wet for too long, avoid the panic response of drying the tape as quickly as possible. Tapes don't respond well to rapid changes in humidity and temperature and trying to dry the tape too fast may make a bad situation worse. (Oh yeah. Drying a wet tape in a microwave oven is right out. Don't ask me how I know this, just don't do it, okay?)
The other thing to keep in mind is that waterlogged tapes can hold a surprising amount of water, and that it's likely to keep seeping out for some time. If you have to send the tape out for recovery, make sure you put it in something waterproof and well padded so the package doesn't disintegrate in the mail.
Emag, a vendor of storage devices and related services has advice on dealing with damaged tapes at: www.emaglink.com/dataRcvPrecaution.htm.
Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.