Rat Water Dispenser

I designed this to use as a second water dispenser for our rats. We have one that is a bottle and a tube, but I'm not sure it's always working. Having this in the cage gives me peace of mind. The base always has 1/4" of water in it, until the bottle is empty.
I designed this so they had enough room to drink, but not enough room to stand and pee in it. The rats seem to prefer this dispenser over the tube type, even though they do get some of their bedding in it.
I designed this to be hard to tip over. When I first put it in the cage, one rat jumped on it. It didn't tip over. As the Rats get bigger and the water gets more empty, the story could be different. I may have to enlarge the base.
I've had water in it for several days and see no signs of leakage.

Update 8/24/14 The rats found a way to pee in their water, so I've posted a new base that only has a small hole exposed for drinking. The rats can easily lap up water from the hole, but so far they haven't had good e