My sister is going to make a batch of wine tomorrow from a kit. She accidentally bought purified water instead of spring water,
Go out and buy Spring Water. Easier, cheaper. Just look at it this way: 6 more gallons of water less than $10, Screwed batch of wine...what 70 to 180 depending on the kit? The time you spent researching this I bet you coulda bought the other water already.
You can use the purified water for mixing up your sanitizer.
Of course, but then I wouldn't' learn anything. I brew enough that I don't want to be stuck buying spring water all of the time. It's enough money and waste of containers/time, plus I have no guarantees of consistency on the source (maybe I could research this). Being able to throw a tablet in some water the night (or 24 hours before I brew) seems a whole lot easier.
Until this point I had always assumed that the chlorine in the water was reduced/eliminated just by bringing the water up to temp for my mash/sparge. I had no idea about the chloramine in my city and lower degree of efficiency of boiling for removal.
I know I could invest in some type of filtration system, but then I have to worry about other minerals being stripped from the water.