I tend to retain water (not just in my hands) for a variety of reasons, so I'm always on the lookout for tips to get rid of it. I haven't found anything that always works, but I've found some things that help.
In my experience, fluid intake is the most reliable. Tea or seems to work better than plain water. With the tea, it might be the caffeine.
Lemon or lime added to the water or lemonade made with real lemons seems to help too, but that may just be because the flavoring encourages me to drink more.
I gain a lot of water with TOM, and last month was worse than most, and although I'd been careful with my calories (so I knew it wasn't "real" weight gain), even after TOM was over, the weight wasn't coming off. I attributed it to the hot weather (because I also seem to retain more water in hot weather).
I happened to have checked out several books from the library on water exercise and water exercise for fibromyalgia and arthritis... In one of the books, I read that being in the water can reduce water retention. Something about the pressure of the water on the skin, actually "pushing" extra water out of body tissues and into the bladder (where it will be removed when you pee).
I was skeptical, but figured it was worth a chance (especially since I like swimming anyway), and I dropped all the extra weight (about 4 lbs of it) by the next morning.
Coincidence? Quite possible, but it has given me another reason to use swimming for exercise.
It's not a really practical solution if you're not fond of swimming or don't have easy access to water, but if you do like to swim (or tread water), it can't hurt.