Fault zones in the upper crust are typically composed of complex fracture networks and discrete zones of altered fault rocks. They generally show a spatio-temporal evolution from the protolith to the fully developed fault with a zoned internal architecture. Distinct domains of fault zones, in particular the damage zone, often represent important areas of essential subsurface water conductivity. Other domains, e.g. the fault core, may act as barriers. Massive influx of water during subsurface excavation is often related to fault zones. To establish a hydrotechnical quantification of tunnel-sections it is important to define the hydrogeological setting. A detailed collection of the hydraulic effectivity of faults is therefore very important for the hydrogeological prediction during the site investigation in view of geotechnical projects.