The paper describes the root causes of damage to an underground potable water reservoir. It is made of reinforced concrete and consists of two chambers founded on subsoil diversified for its age and origin (folds of glacitectonically disturbed septarian clays and postglacial loams). The documented damage results from subsoil deformation caused by volumetric changes in the ground (shrinkage and swelling) due to the facility's exposure to various external factors determining the phenomenon’s intensity for over one hundred years. The analysed example presents problems arising from founding the facility on expansive soils. It highlights the hazards resulting from negligence in landscape architecture development and emphasises the role of identifying the subsoil. Comprehensive geotechnical examination and geophysical measurements of the structure and subsoil, making the inventory and evaluating the nature of the damage helped identify the potential factor detrimental to the facility’s technical condition. The conclusions are confirmed by numerical simulations, which include the impact of swelling and cyclic loads resulting from the facility’s function and surroundings.