Adding coolant question???/

[Meat Head]

My coolant is slightly below the minimum hash mark and I'm wanting to add a little coolant. My question is.......

Would you just add a little distilled water or would you buy a liter (from Pelican) of Porsche OEM coolant?

Is it important to use OEM Porsche coolant or is there an aftermarket equivalent?

Where is the best place to purchase coolant?

Thanks for your input.