Changing coolants question

[Zonaman]

I'm getting ready to install my ac system next week and (since the old heater core goes) thought that would be a good time to switch from Dexcool to the green stuff. So starting tomorrow I was going to drain and flush the radiator, fill it up with water, drive around with the heat on, then drain and flush again-run a few erands or drive to work, and repeat till there's only clear water coming out. There's certainly no danger of freezing here in Phoenix but I just wanted to check with you guys. Since the water pump gets some lubrication from the coolant, would a hundred miles or so of mostly water in the radiator damage it or anything else?

Thanks in advance.