Distilled Water (Demineralised Water)

Minerals in hard tap water can leave scale in the radiator and heater core. Concentrated coolant is often mixed about half and half with it, as the label specifies. Most modern car batteries are sealed and never need topping up. Demineralised water is also useful for rinsing the car after washing to avoid water spots.

Without dissolved minerals, the water leaves no deposits and does not react with the coolant additives.

Do not use it neat in the cooling system; it gives no frost or corrosion protection on its own. If unsure, buy ready-mixed coolant that matches the car’s specification.