Malaki ang margin of error ng coolant mix. Anything from 40% to 60% will work. Manufacturers just peg it at 50% for convenience. It will not be 'walang silbi' if you don't mix at exactly 50%. It will not eat through a gasket or destroy a radiator unless you intentionally use a 100% coolant concentrate without any dilution.

I used a mix of distilled drinking water and coolant.

Pero for top ups, I just use tap water. Bihira lang naman mangailangan ng top up ang Pajero. (once in 3 months? wala pang isang tabo).