If he has spent any time in his water, it should be changed within the day. Get a water testing kit from the pet store/aquarium supply and see how bad it gets after he is in there for just a few minutes. If he is burying himself that much, his dirt may be too dry, even if the air is high enough humidity, he will always want to burrow, and if the soil is pulling moisture from him, he will think it's time to aestivate