[Sebnagy22]

Need to top up my engine coolant on my 428i and I got some OEM concentrate that needs to be mixed. The technician at the dealership said they use regular tap water when they replace it/top it up on cars. Should I use distilled water or normal tap water to mix it? I'm not sure if I can get hold of distilled water unless I order online *

[obert]

Pretty sure it calls for distilled water.

[Billfitz]

Depending on the mineral content of your tap water using it can cause everything from mineral deposits on the heater and radiator coils to system corrosion. Distilled water is cheap insurance against that. I get mine at my local grocery.

[Sebnagy22]

Originally Posted by Billfitz

Depending on the mineral content of your tap water using it can cause everything from mineral deposits on the heater and radiator coils to system corrosion. Distilled water is cheap insurance against that. I get mine at my local grocery.

I went and got some de-ionised water, same thing as distilled pretty much

[Billfitz]

De-ionized is OK, as it has metal and mineral content removed via filtering. Distilled is higher in purity, but it's more expensive, and the purity of de-ionized is adequate.

[pierreye]

Just get battery top up water. It's basically just distilled water.