The most common description of a Ball python's natural habitat is "dry grassland". And I'm pretty sure they have a dry season as well as a wet season. I've watched a few videos of balls being harvested in the wild and don't recall seeing ponds or creeks...
The area may have a very dry season but I promise you the inside of a termite mound is maintaining some wicked high humidity for most of that season, you know? As in condensing on the walls kind of humidity.
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