The wort cannot be cooled below the cooling water temperature. While the Therminatorâ„¢ is the highest-capacity homebrew chiller on the market, it will get you within a few degrees of your cooling water. But if you live in a warm climate area, that may not be enough. To drop below your groundwater temperature, you will need to use a cooling water pre-chiller. This is simply a 5/8" copper coil (25 to 50 feet) immersed in a pail of ice water. Use this to cool the groundwater before it enters the chiller. Stirring the ice water is recommended.