Another source for what is basically distilled water is the ice build-up you have to chip away from a freezer.
(De-frosting a non, frost-free freezer, of course). If you're in the city, I'd just buy the distilled bottled water.
I suppose the photography folks living in Bermuda have it easy, (for distilled/demineralized water),
as the Island's entire water supply is captured rain water.