Mine will do this as well. If you had the option between a glass of water a day old and a glass of water just freshly poured, I think we all know which one we'd choose.

I think all animals are the same way. One of my cats, Liam likes to lick water from the tap and shower water on the side of the tub (with no soap in it, don't worry) all the time and prefers it over the water offered in their bowl.

I've been using tap water for the past 5 years with my snakes and have never had a problem. Bottled is unncessary but some people preferred to use it. Of course, watch which bottled water you use. I work with someone who used to work in a water testing facility where they test the contents of bottled water. She says most bottled waters are the same as tap, just in a plastic bottle. She said some even contain trace amounts of feces.