Ideally, this would be distilled water. You can also use bottled water or tap water. Bear in mind that tap water or bore water contains minerals that can leave deposits throughout your cooling system, contributing to corrosion and reducing the lifespan of the radiator.

What water do you put in engine coolant?

You can buy it pre-mixed but if you feel comfortable making your own it's always best to mix the antifreeze with distilled water before you put it in. Most labels recommend half and half as a measurement but in the really cold month's experts recommend as much as 70% anti-freeze, 30% distilled water.

Can I use bottled water for engine coolant?

While some engine coolants are designed to be mixed with water before being poured into the cooling system in your vehicle, you cannot just use any water that you please. Tap water is full of minerals that will eventually form deposits inside your radiator, plumbing and water pump.