Rock groundwater has always caused major problems when tunnelling. Water leaking into tunnels can cause large problems, not only on the construction itself but also on the environment. A continuous water leakage can lead to a declining water supply, and geotechnical problems can occur as subsidence in the ground. Therefore it is of great importance to predict the consequences that can appear in the surroundings due to a declining groundwater surface.The aim of the study was to investigate different methods for predicting leakage and changes in groundwater level due to tunnelling excavations in rock. This thesis was performed by comparing mathematical methods, actual groundwater changes and results from preliminary investigations.Investigations were made for three railway tunnels planned by Botniabanan AB.