Angel - I said check for mites, not that it had mites, and it is not a "ridiculous assumption".
Ball pythons are not an aquatic snake. They live in rodent burrows.
When a snake has mites, very often they will soak in the water dish as it kills some of the mites that are on them and pestering them. That is why it is a good idea to check for mites when a non aquatic reptile is spending a large amount of time in the water.
Sure - snakes have different personalities, but for a ball python to remain in the water all the time is not normal ball python behavior, except when it is getting ready to shed or has just eaten a particularly large meal. There is probably something about it's habitat or health that is causing this odd behavior.
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13. My BP sits in its water bowl all the time. Is this normal?
No. A ball python will usually have a specific reason for soaking. There may be problems with the temperatures in the enclosure, or it is trying to get off stuck shed, or it is trying to drown mites.
from http://www.ball-pythons.net/forums/showthread.php?t=31102
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OP - you mention you are keeping it with another ball python. Are you sure you have adequate hides for both of them? It may be using water as a place to feel a little more secure than just being out in the open.
I agree that it is generally not a good idea to house ball pythons together except during intentional breeding, especially when one them is exhibiting non normal behavior.