There was a discussion a while back about using WaterWetter + distilled water only. It was advised that a small percentage of normal coolant be added as well, for its anti-corrosive properties. This is particularly important in a street driven car, which only sees a coolant flush once in a long long time. Race cars use WaterWetter + distilled water only, because they are frequently stripped down and rebuilt, thus no worry of corrosion.

From memory the recommendation was 20% WW, 40% distilled water, 40% coolant.