water

I use water straight from the sink, which is well water. I do get it tested every year, but that's really for my own safety just in case the well gets contaminated.

I asked my vet this question once. He said if its good for you to drink its alright for the snake.

Well, if tap water is good enough for me, it's good enough for my :snake:.
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Give them whatever you feel most comfortable with. You are the only one who knows the quality of the water that comes out of your home tap. If it's not good enough for you to drink then you probably wouldn't want to give it to the snakes. I drink the water that comes out of my tap and it tastes fine, that's what I give my snakes.