If you have tried all possible solutions and the water glitch persist, and you get freezes here and there:
Go to recovery console and do step 3.Restore File System, and 4.Rebuild Database *
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- Re-install the main game with the patch, and re-install Dawnguard as well after that.
- Load a save without having fortify potions.
- Travel with that save to Dawnguard and see what happens.
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* After that turn your PS3 off from behind if you have the fat model (switch 1 - 0).
If not after you have turned it off from the XMB - pull your power cord from behind and leave your console off for 1 hour.
Then insert the power cabel again turn it on and do the above suggestions.**