As far as I know there is no way to make tap water as pure as Distilled. I looked into it very briefly for my Reptifogger and decided that I was fine spending about $2 a month on water to save myself the headaches of trying to clean up the tap water.

J Teezy nailed it on the head. I get my Hydroton from a nursery near my house, it is considerably cheaper the the ZooMed Hydroballs!