With the DeMarco patented system (patents #6604376 and #4538418) from Encore Energy Systems and American GeoThermal Systems you don't need a buried horizontal water loop field or a series of vertical dry wells connected by pipes. Instead it uses the otherwise wasted thermal properties of water in the mains.
The DeMarco Energy Miser System features an heat exchanger that transfers heat or cold from the municipal water supply to a closed loop system inside the building. Without a buried geothermal pipe system all the benefits of geothermal HVAC system are still obtained: low operating costs, flexible temperature zoning, high efficiency even when temperatures outside are at extremes, and free hot water heating during the cooling season.
But the system has one more benefit: it is scalable. To add capacity to a ground loop system another ground loop must be buried but with the DeMarco system a valve is merely adjusted to allow more flow from the municipal water supply.
The system works using effluent, grey water and recycled water (such as that which SAWS distributes to industrial users) as well.
To test the system the company chose locations with extreme weather. Fort Irwin National Training Center (Dry Heat of the Mojave Desert), Winner School District 59-2 in South Dakota (Extreme Cold) and the Marine Corp Air Station at Beaufort, South Carolina (Extreme Humid Heat).
A study by R Gordon Bloomquist, of Washington State University, for the Department of Energy (Municipal Water-Based Heat Pump Heating and/or Cooling Systems DOE /ID/13480--T/) found that such a system would not adversely affect the water system from which it drew heat or cold. You can view and download a copy of the report from the OSTI.gov or Science Accelerator site.
Since the system requires the cooperation of a water provider, the initial prime market is state, federal and city owned buildings, large campus facilities, entire smaller cities or communities, buildings centrally located in the water distribution network, large master planned communities and sites with grey water or reclaimed water supplies. But once a water utility had experience with it, they might be inclined to allow individual homeowners to install it as well.
Several years ago our members heard about community wide geothermal from Victor DeMarco. The work seems to have progressed and seems to be gaining some momentum.