recently installed a water source heat pump. We take water from a borehole and return it to the River Teviot through the garden. It is working well, despite the fact this was a retrofit and we are using conventional radiators. We were also able to ge the SCRI grant even though water source heat pumps are not listed as eligible - it seems they are fine for Scotland, though these regulations may since have changed - we fitted ours in Nov 2007
If your house is modern (mine is 8 years old) and your radiators adequate with your old heating system, then water source heat pumps will work - they are more efficient that ground source ones. I have heard others say that all you need to do is oversize your radiators and they will work with any heat pump system. However, from the cost point of view, it's only worth doing if you are not on mains gas.