Generally, you do want to treat the tap water. There's a lot of junk in our water that makes in bad for frogs, even in countries with super "clean" water, like Sweden. Sure, it's "clean" for us, but it's not clean in terms of chemicals and things like that. I personally think it's a no-brainer. If it CAN be dangerous to not treat the water, then just treat the water, nothing smart about taking the risk. There are different kinds of conditioners, just pick one. I know many people that have used Zoomeds with great success.
ReptiSafe

There's a great sticky topic on this very subject with a lot of great information. Be sure to check it out:
http://www.frogforum.net/vivarium-te...hing-else.html