My suggestion. I use to keep herps before i switched to dart frogs. Chinese water dragons do like water, but they also get to around 3 feet long. If you are looking for a really cool lizard that works well in groups and also can swim really well and will spend a lot of time either on land or on water, i would go with Fire Belly Newts. They are pretty cool, easy to care for and normally pet stores have them and they are only about $5-10 each. I had a bunch of them in one of my big terrariums. Great lizard to keep.
Most other lizards can handle water, but generally wont care to have it. If you are doing half water i would avoid a "general land lizard" because most of them dont swim well and the only ones that generally do are fairly large.
Just my opinion. If you have any other questions hit me up with a pm or ill check in on this again sometime.
Good luck!
Wayne