Q&A

What we now call 'coolant' and 'antifreeze' are the same thing. The old word is 'antifreeze' because people used to use alcohol in the cooling system to avoid freezing, but no more. We use a multipurpose 'coolant' concentrate which you dilute 50% with water to use. You use a 50/50 mixture of coolant and water. If your local water is hard or acid, it's better to use purified water in order to avoid corrosion.
If you just have to add a little, coolant straight from the bottle is OK or good quality drinking water. Doesn't make much difference in small amounts but if you're worried about the coolant reservoir freezing, use coolant so it won't freeze and damage the reservoir.