Just thought I'd give my 2 cents as I didn't want to read and run
Daily weighing is evil lol Like you said, it plays such mind games that it effects your mood.
But look at the bigger picture - the very last figure your scales is giving you is only ounces. And since you know that it can't be a fat gain and is almost definitely a water gain, why let 4 ounces of water take enough power to get in to your head. I totally understand that the numbers going up, no matter what the reason, can play on the mind though, but since a low mood can make us want to binge, it can be a slippery slope.
What I try to do (apart from doing my best not to weigh daily), is to take a step back, breathe, and try to put it in perspective. I think another good thing to do, if you've had a slight gain, is to think 'right ok, that's my number right now, but I won't let a number affect me. How do I actually feel today? Any lighter? Smaller? Fitter?' It may even help to think about how you actually feel and get that established before you weigh yourself, that way, if the numbers aren't what you wanted, you can immediately take the control away from any potential negative thoughts, and have a better day
Sorry for the rant lol x