Condensate porosity in porous materials has a significant influence on comfort, energy consumption, and material’s strength and durability. The variation of the moisture content of the material for a given variation of relative humidity describes the moisture storage capacity and has to be determined experimentally through the water sorption isotherm. However, the characterisation of sorption isotherm is very time-consuming, mostly for high relative humidity conditions, which may cause experimental errors and reproducibility problems. This paper aims to estimate experimental water condensate porosity using mercury intrusion porosimetry and nitrogen adsorption technique considering pores smaller than 0.1 μm for a wide range of porous sedimentary rock types with different petrographic characteristics. Particularly for nitrogen adsorption characterisation, we interpolated the pore volume using BJH method applied to the desorption branch. In the water adsorption test, condensate porosity is obtained with the maximum adsorbed water at RH = 100%. The ratio between water condensate porosity and total porosity in the studied porous stones is important and varies from 2 to 38%. Nitrogen adsorption technique provides the best estimation of condensate porosity (R² = 0.979) and an effective estimation of water condensate porosity. The correlation between condensate porosity using MIP is moderate (R² = 0.892) and presents a wider dispersion for all the range of condensate porosity. A mathematical expression that fits the shape and curvature of the water isotherm was also analysed in terms of pore structure. These studies are scarce for porous stones and our results provide valuable information for these widely used construction and building material.