My old Toyota Corolla LE didn't have an evident/separate engine coolant reservoir. I usually go with the traditional way of opening up the radiator cap and filling it up with distilled water before I go or if I left the car in a parking lot for 6 hours or so.

I recently retired my Corolla and have replaced it with a Hyundai Matrix CRDI. It has a transparent engine coolant reservoir which the manual says, should be filled up between the full and low mark. Whenever I open up the radiator cap, I could see a blue-green liquid substance, which I assume is the coolant.

Do I have to put distilled water in it or does checking the engine coolant level enough? Or do I have to fill the engine coolant reservoir with a dedicated coolant and the radiator with distilled water?

Sorry if I sound vague. This setup is new to me.