I figure my response will either be competitive or will get me banned (maybe both!)... Well here goes:
While spritzing flowery-smelling water on your tender "lady parts" may be sufficient to get THEM clean, a carboy needs something a little more vigorous!
My post-fermentation carboys are...
Distilled water IS right at 7pH but that is neutral, not acidic. As for "keeping" it, at 89 cents a gallon what's the point? +1 on mixing up some Starsan...
Mals