Water quality is a frequently overlooked issue in the application of geothermal heat pump (GHP) systems. When considered at all, is often viewed as a problem unique to open loop systems. In residential open loop applications water is supplied directly to the heat pump’s refrigerant-to-water heat exchanger. If the water has a tendency to be scale forming, fouling of the heat exchanger may occur. This fouling reduces the effectiveness of the heat exchanger and compromises the performance of the heat pump. Water quality is also a consideration for closed loop systems. In the closed loop system, the concern is not the main refrigerant to water heat exchanger but the desuperheater