Soil works as a source and a sink of heat due to its high thermal inertia. Coupling buildings to it using earth-to-air heat exchangers has been widely used to heat buildings in winter and cool them in summer. Several methodologies have been developed to simplify design strategies and optimize the performance of this technique. Recently, researchers have proposed the use of water as a heat exchange media with the soil. In this study, the use of buried water tanks as thermal accumulators is proposed. An experimental prototype to examine heat exchange between the tank and soil was built. The data obtained allowed a real-scale estimate for the water tank. Heating and cooling power outputs used as a reference value for the real-scale estimate were obtained by simulations in the EnergyPlus software, which calculated the power requirements to keep up a building at 18 degrees C in winter and 25 degrees C in summer. The greatest heat exchange rate was 24.66 kWh/day. The experiment proved that the proposed technique is reliable for the natural air-conditioning of buildings and to overcome the constraints imposed by the traditional ground heat exchange systems. (C) 2018 Elsevier Ltd. All rights reserved.