This work focuses on 3D groundwater modelling as a predictive tool to assist in the design and optimization of the dewatering system to be installed during the construction and operation phases of a dry dock. In order to simulate the 3D groundwater flow conditions, finite-difference numerical models in steady-state were generated. The simulations allowed for the evaluation of the hydrogeological conditions and the quantification of water inflows to the excavation and drainage system planned under the designed bottom concrete slab. Vertical upward hydraulic gradients and total hydraulic gradients were analysed as well, aiming to prevent potential limit states related to hydraulic heave and internal erosion.