Originally Posted By: Gebo
I have a reverse osmosis system for my saltwater fish tank. It is absolutely perfect for your coolant mixing. It removes “all” minerals.
Something I did was use an empty gallon milk jug and pour 1 qt of water in it. Take a marker and make a line at that water level. Pour another qt of water and mark that level, etc. I ended up with lines ar 1,2,3 and 4 qts. Then it was so easy to make my 50:50 mix of coolant and be consistent in adding it to my coolant system. I’d wait and fill up my reservoirs last.
It's easier than all this... just put a sharpie mark about halfway up. Fill it that far with water and dump your pure antifreeze in up to the top. (And by "top" I mean leaving a little air space like it originally came with.)
Then refill your antifreeze bottle with water to its top. Mark both as 50/50 now so you don't forget.
One bottle might be 45% strong and the other 55%. No worries!
Alternate a quart from each into your car. When you get down to 1/2 gallons pour the milk jug back into your AF bottle.
RO is a completely legit demineralization.
I use hose water but my private well is between a couple of Poland Spring bottling plants.