Several of my neighbors are scientists and research Dr's and all of their labs have the equipment to purify water to "laboratory" grade. They have explained the process at length, although I don't remember the particulars, and it is a much different product than anything you can buy in a store.
I rotate who I ask, but they all are great about getting me a few quarts at a time to clean my vinyl. The hardest part is getting a container sterile enough to put it in. I give the the bottle, and they sterilize it again prior to putting the water into it.