Based on recommendations from Stewart Water Pumps (have one on my Corvette) I am running straight distilled water with nothing else but a bottle of Prestone water pump lube/anti-corrosion. Temps are ridiculously low even here in Houston, although it's not the hot season yet...
Some claim that water wetter is causes lubricity problems. I do know that a freshly rebuilt water pump didn't last 500 miles when I was running water wetter and distilled water, failed bearing. Not sure if that was the cause, although the pump was a professionally rebuilt GM housing.
Jeff