I don't carry "crap" discs for water except on a few very specific courses that have water+high wind in play simultaneously.
I have however, learned not to throw favorite or really expensive discs over high-risk shots (Don't throw your translucent 2nd run CE Valk on a forehand helix over a pond into a headwind, for instance).
I am a huge fan of X-out Champion discs. You can get some of them for as little as $8 (most are $10), and they fly great. That way, I can throw my main driver, and if I lose it, oh well --- I'm only out $8-$10. But my odds are high of making the shot, since I am throwing a disc I know and like.
I've got several backups of X-out Teebirds, Destroyers, Firebirds and Orcs -- these are what I throw 90% of the time on my drives, and 90% of the time over/around water as well.