It is highly desirable to localise and quantify water inflow zones in front of the tunnel face using indirect methods without any interruption of the excavation process. The spatial temperature field in the subsurface is influenced by water circulating in extended zones with a natural velocity of more than 10-8 m/s (~1 m/year). This allows to characterise the hydrogeological conditions by rock temperatures measured along the advancing tunnel. Such temperature represent a one-dimensional data set only, their interpretation cannot reveal the spatial characteristics of water bearing zones. Since for tunnelling only the water-bearing zones ahead of the advancing face are relevant, the following procedure is foreseen: First the rock temperature prediction along the planned tunnel trace is calculated with a 3D FE model based on heat conduction.