This study reports on the actual energy and economic performance of a water source heat pump recently installed and operated at a Glasgow Subway Station using subsurface water ingress to provide heating and domestic hot water. This follows from a previous publication (Hytiris et al., 2016) that detailed the empirical measurements and design of a heating system designed on the basis of a fifteen-month monitoring period of the water flow and temperature. The perennial water flow at a relatively high temperature enabled the system to operate more efficiently than a typical heat pump system with boreholes or trenches. The performance of the water source heat pump has been monitored for a four-month period and the coefficient of performance as well as energy saving is reported in the present study. The findings of this study indicate the energy, carbon and financial benefits of the heating system, but also highlight key issues during the operation in such a demanding underground environment. Further renewable heat potentials for the rest of the subway network and opportunities to commercialize the excess heat energy output are explored.