The pumping of groundwater near GHEs improves the performance of GSHP systems due to the advection of the induced roundwater flow when the hydraulic conductivity of the formation is favorable. To quantify the effect, we first carried out performance analysis of a GSHP heating system under the influence of groundwater pumping. The heating operation data clearly showed the improved COP of the heat pump when the groundwater is pumped. To evaluate the effect of groundwater pumping, we then collected the water pumping data from the groundwater snow-melting system in Akita City, Japan and input those data to the existing field-scale numerical groundwater flow and heat transport model of the area. The model was run to calculate the groundwater velocity and temperature in the area under the influence of groundwater pumping. Then, the output from the model was used for developing another numerical model, small-scale GHE model, which can estimate the minimum necessary GHE length for a Japanese standard detached house at several locations in the area. The GHE length data were mapped using GIS software to generate the GSHP potential map under the influence of groundwater pumping. The comparison between the potential maps with and without groundwater pumping clearly indicated the contribution of water pumping in reducing the GHE length and the initial cost of GSHP systems.