I have a refractor, and once I even had to take the objective apart, there was a fungus growing between the crown and flint elements, but I do have high quality mirrors in my right-angle diagonals and there are erecting prisms. Distilled water cleans and lubricates gentle wiping so that anti-reflection coatings are not damaged. When I owned an 8" reflector, the whole mirror could be submerged in water to remove grit and condensed dew grunge without scratching the metal. And then you just leave it out to dry to get rid of the excess water.

As for the yuppy water, the distilled water is bottled by the same manufacturers and stocked on the same shelves as the "pure drinking spring water", even the packaging is very similar. I think the major determinant in what it costs is what yuppies are willing to pay for it.