AbstractWater is an important weathering factor that can play a role with respect to rock discontinuities, and thus rock mass behavior. The increase of rainfall (frequency and intensity) highlights new problems concerning rock mass stability. The aim of this research is an analysis of the importance of the role of water on rock alteration. This study will discuss how water causes discontinuity degradation, which can affect the stability of the rock mass. The accurate study of water-rock alteration is based upon two aspects, on the one hand the study of the intrinsic properties of water, and on the other hand, the study of the response of the discontinuity to alteration. The present study is based on two spatial scales, laboratory and in sit...