Ground-coupled heating-cooling systems (GCHCSs) exchange heat between the built environment and the subsurface using pipework buried in trenches or boreholes. If heat pumps in GCHCSs are powered by "green electricity," they offer genuine carbon-free heating-cooling; for this reason, there has been a surge in the technology in recent years. Interference between adjoining installations is being reported, raising issues of sustainability in terms of performance, equitable sharing of natural resources, and localized ecological impacts. Using an analytical model for heat transport in porous media, sensitivity analyses have been obtained for open-loop systems in typical hydro-geological settings for urban GCHCSs in the United Kingdom, revealing that breakthrough of injected water will likely lead to significant declines in system performance in less than 25 years for well spacings less than 300 m, unless injection rates are kept below 250 m[superscript 3]d. Only by cooperatively planning will adjoining landowners in urban areas achieve large-scale sustainable system designs. (Contains 4 figures.)