Cu-BTC metal–organic framework (HKUST-1) was evaluated as the model material for CO2 capture from flue gas streams. This paper presents an optimised hydrothermal synthesis of HKUST-1 and an analysis of water stability of HKUST-1. Substantial improvements of the hydrothermal synthesis process of HKUST-1 are shown to increase the quantitative yield up to 89.4% at 100 °C. Single-component adsorption experiments were carried out under conditions relevant for flue gases adsorption (45–60 °C, 0–1 barG) to evaluate the performance of HKUST-1 in terms of adsorption capacity, showing that the amount adsorbed of water can reach up to 21.7 mmol g−1, about one order of magnitude higher than CO2 (1.75 mmol g−1) and almost two orders of magnitude higher than N2 (0.17 mmol g−1). The hydration process of HKUST-1 framework was investigated using dynamic vapour adsorption under the flue gas emitting conditions. HKUST-1 is sensitive to humid streams and dynamic deformation of its porous structure takes place at 40–50 °C and various relative humidity values, leading to the irreversible decomposition of HKUST-1 framework and the consequent deterioration in its adsorption capacity. Under humid conditions, water displaces the organic linkers from the copper centres causing the collapse of HKUST-1 framework. These results provide fundamental knowledge to enable future material design for the modification of the hydrophilic nature of copper sites in HKUST-1 to improve its moisture stability.