Which types of water supply is not recommended for heat loops encased in a floor?

The use of solar panels in water supply for heat loops encased in a floor is not recommended primarily because solar panels typically collect and transfer heat from sunlight to a working fluid, often resulting in water that can be too hot or contain impurities that could damage the floor heating system. Additionally, the water circulated from solar panels may not provide a consistent or controllable temperature necessary for efficient heating.

In contrast, other options like groundwater, city water, and rainwater, while dependent on specific conditions and treatment methods, are more suitable as they can be regulated and treated to provide the appropriate qualities needed for a heat loop system. Groundwater can generally maintain a stable temperature, city water is often treated to ensure cleanliness, and rainwater can be collected and filtered for efficiency in heating applications. However, it's crucial to ensure that any non-potable water source, including rainwater and groundwater, is adequately treated to prevent issues with mineral buildup or contamination.