That's exactly what you're not supposed to do. Tap water has deposits in it that will eventually cause clogging, especially in the heater diverter valve. I've rebuild about 6 of them now, and besides the green coolant drained from them, I can also tell who's been using tap water w/ the wrong coolant. There is a reason why you're supposed to use distilled water, just like you're only supposed to use phosphate free coolant. Not trying to be an ass, but you just wasted your money by not spending an extra $2.

__________________