As Ph goes acidic, the cooling system turns into a battery. As in, you actually start measuring voltage in the water. And this is what causes the really bad corrosion.

Mine is still on the original water pump from 2003 w/ 109k miles I guess I should change it next time I'm in there if it hasn't failed by then...

Exactly and the corrosion is what kills things.

When I changed my belts at 60K I found that the original water pump had been leaking enough to stain the drain. At the same time I changed all coolant hoses and found a (maybe not alarming) surprising amount of corrosion on steel hose fittings. I blame this on the factory antifreeze fill. At 120k and another hose change the amount of corrosion using aftermarket antifreeze was unchanged from 60K. So, if you still have the original antifreeze in the car get rid of it.

All this talk reaffirms my decision to not use water. it's nice to not worry about any of this.

On my AWD DSM, that I bought new, I changed the water pump every other timing belt change: 120K miles. I used OE Mitsu parts and no issues, they never showed any sign of leakage when removed. Drove the car 313K miles. But I'm older and wiser now, so I changed the water pump on my Evo when I changed the timing belt- for the reasons mentioned. And will continue to do so. It's just too much work doing everything again if it failed later. Deionized water is supposedly the best for mixing with coolant.