Groundwater systems are much better. My parents house in Ottawa has one, and it works fine through -30 C nights. There's a source well about 30' deep with a pump at the bottom, and a return well some distance away. That provides a constant supply of water around 5-10 C for the heat exchanger.
It is a complicated system -- lots of valves and reservoirs and so on, but very efficient and doesn't need much maintenance.
It is a complicated system -- lots of valves and reservoirs and so on, but very efficient and doesn't need much maintenance.