we have a young BP. about 18" long and 2thumbs wide....
Water bowls can be as big or as little as you want them to be.
If your snake soaks on their own during the shed cycle, get a bowl big enough for them to fit in. That's the general rule that applies.
Otherwise, you just want a bowl big enough to hold a fresh supply of water and help bump up your humidity if necessary.
we have a young BP. about 18" long and 2thumbs wide....
Well ball pythons dont really need big water bowls...a healthy ball python will rarely soak in its water bowl only if it has mites, the humidity is too low, or if the hide is too hot...ball pythons only need a bowl that can provide fresh water...
Usually with BPs, you will want to choose a water bowl that helps you maintain the proper humidity. As Psycho said, BPs usually don't choose to soak unless they have mites or some other issue.