I usually have some distilled water around, so I suggested that.
Between acid rain and the minerals in the water when you wash your car, I don't know why you'd bother with distilled water in something like this.
I certainly understand there are situations you absolutely want to use
distilled water, where minerals and such could clog up a system (e.g., you DO NOT want a water/methanol injection system to fail due to a clog), but water with minerals on it getting on your paint? Meh. Save the hassle of buying/transporting/storing distilled water for where it's really needed, IMO.
Certainly, distilled water in your mixture is not a bad thing. I just prefer to have a supply handy for when it's needed
, rather than needing it (and not having it) as a result of unnecessarily using it, thus requiring a trip to the store.