because if you need to use it in your cooling system of your vehicle, you should use dH2O, otherwise you will need to flush the system to avoid corrosion. But any water will work in emergency. I buy distilled water for 83 cents/gal at the grocery store; I also have methanol/water injection in a couple of my toyotas which requires distilled water to avoid corrosion also. but having water is the important thing, without that you're not gonna make it very far. Wanna kill these ads? We can help!