Soft Drinks, at least in the 100 or so bottling plants that I know do not use distilled water. They use filtered water.
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Are these particulate filters or reverse osmosis filters, which can make water 99.9% pure? Starting from scratch, all water is pure, or distilled. Percolate it through a couple hundred feet of bedrock and it bubbles to surface as hard well water. Why would it make a difference if we purified it and then poured in the magical ingredients it takes to turn it into Coke Classic? Of all the things I have to worry about, it sure wouldn't be that my cola is too pure and may leach minerals from my body. Let's just say that too much of anything (water,pop,beer) is bad for me. Back to the radiator. Put in distilled water. Any dissolved salts are going to contribute to scale. The anti-freeze you put in will combat the corrosion issue and provide pH balance. No acidity.
As for "Not For Human Consumption" there are stringent regulations to meet (Federal,Provincial,State) in order to sell drinking water. They probably didn't want the hassle. Ever hear of Walkerton, Ontario? People died due to lax adherance to regulations.