Do you mean he doesn't sit in her water dish? If he is eating, peeing and pooping, and active, he may just not feel the need to sit in there. He's from a very dry climate, not a lot of water access. My Russian has never once used the saucer we have for her in the yard.
If you want to make sure he's getting a chance to soak or drink, do ia soak first thing in the morning, before he gets warm and moving around. Put warm (but not hot) water into a container he can't see out of. Make sure the water doesn't come up past the line where the top and bottom shells meet and gently put him into it. Observe from a bit of distance (don't hover over him). In a few moments he should relax into the warm water.
My Russian rarely drinks even while soaking. Unless she's just come out of hibernation, about ten minutes in the tub is all she'll tolerate.