Pumping ice water through your chiller is more effective than using a pre-chiller, in my experience. I run tap water through my chiller to knock the temperature down to about 100º F, then switch to pumping ice water. I have a submersible 1/6 hp pump I got from Harbor Freight for about $50. I put this into a 20 gallon plastic tub with about 10-12 gallons of ice water and recirculate the water through my chiller to get down to pitching temperature. While I waste a few gallons cooling with tap water, it doesn't take very long to get to about 100º and the few gallons I use to recirculate is quite a bit less than what I would use trying to get from 100º to pitching temp. with tap water, or even with pre-chilled tap water.