As of January 5, 2019 - 01:39, this link is reporting 404 - Not Found.
Ground source heat pumps extract latent heat from ground. They need a large area to dig 100-300 ft. trenches. It is expensive to install, but very efficient. Ground source heat pumps are not very good for very large homes or home with high heating requirements.
Water source heat pump is the same as a ground source heat pump but even more efficient. One needs a body of water ideally at least 8 ft. deep such as a large pond or lake, river or large creek.
Cost saving comparisons between heat pumps and electricity.