The first time I saw any of my BPs drink was today! I was feeding them and I turned around to see my spider girl with her head in her dish! I have 8 snakes and I've only witnessed three of them drinking (two only on one occasion each and the final one drinks IMMEDIATELY after she eats so it's easy to catch her). I wouldn't worry about it! So long as his skin doesn't seem overly wrinkly, he's fine.