Twice distilled water is the way to go

If you guys like water so much you should go here:

http://www.thewaterworksrestaurant.com/main.cfm

I go there from time to time, nothing like sitting down to a $65 bottle of drinking water. Wowaweewah!

Guys - distilled water. Done.

Deionized does cause problems with taking ions from metals and if they're thin enough it can lead to corrosion through the metal.