In general deep ground water and soil temperatures will generally be the average long-term climate temperature. Here in NY I believe we are in the low 50's. Just across the lake in Canada, in the upper 40's. Their tap water feels like ice on hot summer days. Thus geothermal cooling is very efficient and cost-effective in the summer if added to a house of new construction. It is painful to get hot water out of it though, you are right, it is expensive to heat this cold water up! Popular in the 70's was to put solar pre-heaters on the roof, but they were prone to leaks and freezing up in the winter.
