What is the correct coolant mixture to use in the water-cooled Spoolmatic 30W model?

You must use only a mix of 50% distilled water and 50% high quality automotive antifreeze that does not contain stop-leak additives. Using incorrect coolant or coolant containing stop-leak additives can corrode and/or plug gun/feeder cooling passages, and use of other coolant voids the warranty. (Page 3)