While you should use a proper coolant in the radiator, the AC water is a good alternative. Reason being its distilled. There aint any impurities. However, use a cotton cloth to distill it further from any small impurities into a closed water bottle and store it in your car.
Most coolants come pre-mixed but some require missing with water. In that case, you can use the distilled water. Bottled distilled water is expensive when you get it from the market. The AC water is the best alternative in that case.
