It's wonderful that you're thinking about maintenance now!
I wish everyone did -- we'd have a lot more successful maintainers that way. Kudos to you, Ncunceo, for being so thoughtful and perceptive about maintenance. I know you've worked way too hard to ever let this slip away.
Everyone's right, nothing changes. Maintenance looks just like losing, with a few extra calories. You do exactly the same things to keep the weight off that you did to lose it. During your time of weight loss, you've been assembling your maintenance tool box of skills, strategies, and day-to-day behaviors that you'll use every day for the rest of your life. The transition from weight loss to maintenance is seamless.
I've never heard about gaining water weight after one reaches goal and I can't imagine why it would happen. It would be really easy to gain FAT weight, of course!
The good news is that since you're so good at weight loss, you're going to be a great maintainer!