antifreeze

This might be a stupid question but here I go, I am cleaning out the radiator and cooling system of my FE350 -93. Went to the local car spare shop to get some coolant/antifreeze. They asked me what quality that was specified and continued to explain that aluminium engineblocks would have...

For the summer months it is understood that pure water cools better than an antifreeze/water mix. But should distilled water or tap water be used. I have read that distilled water is more corrosive to aluminum than tap water but tap water tends to leave deposits. Is anybody running pure water...