Aluminum heads on iron blocks create enough problems without introducing more by using impurities into the cooling system. If your car is getting up towards 20 years old I would be using every trick in the book to ensure trouble free motoring.

Use the approved coolant. Cheap insurance. By some extra for topping up. ( The Lord only knows what all those added chemicals in the water supply are doing to our human bodies over a lifetime)

In another life I worked in the Asian tropics. Our company installed huge backup power supplies and batteries for our projects. These batteries had a life of 15 years. Injudicious maintenance could shorten the life of these by half. We are talking about battery packs that are larger than a standard W140 S class and costing big bucks.

The air was so polluted in SE Asia by industry and vehicles but more importantly by the hundreds of active volcano's venting sulfuric acid etc etc, that even local spring water first distilled was not pure enough to top up our batteries. Our purified water came from Norway.