[Joe]

Those minerals are the reason not to use tap water. They will do a number of things includind:

1. increase corrosion of Al. and Cu
2. contains a number of different bacterias that will thrive in yer cooling system
3. after time the minerals will deposit them self in a film along the walls of the cooling gear
4. Most pumps recomend using distilled or filtered water.

Its cheap, .25$ for a Gallon at some places.