What is the benchmark for the quality of chilled and condenser water? I believe it is measured in ppm of minerals but what type of minerals should we be removing to maintain the good quality?
I would rather say ions. Primarily, Calcium, Magnesium, Carbonates and Silicates have scale forming tendency (but not limited to). Hardness should be generally below 50 ppm and TDS below 300 ppm (500 ppm is the maximum limit)
Either you can keep control on these parameters are use corrosion and/or scale inhibitors to increase the safe levels.