According to ASHRAE (1999a), the desirable temperature for swimming pools is 27C, however, this will vary from culture to culture by as much as 5C. If the geothermal water is higher in temperature, then some sort of mixing or cooling by aeration or in a holding pond is required to lower the temperature. If the geothermal water is used directly in the pool, then a flow through process is necessary to replace the “used” water on a regular basis. In many cases, the pool water must be treated with chlorine, thus it is more economical to use a closed loop for the treated water and have the geothermal water provide heat through a heat exchanger