The dehydration thing is less likely the issue but just in case it has something to do with it goig on for weeks now.. Some snakes are very very picky about their water. In fact most bloods and borneos refuse to drink water that is more than a day old.
Some of my balls are that picky. They will not drink unless I rinse the bowl every day and refill it.
Try this. If your temps are right in the tank try fillling it with water that is a little cooler than room temperature but not cold.
Some snakes are picky like that.