By providing high surface areas with tunable uniform pore sizes and well defined acidic moieties within the pores, organic acid functionalized mesoporous silica has attracted attention as a substitute for homogeneous mineral acid catalysts in liquid phase reactions. Exploitation of their potential for catalysis will necessitate characterizing their acidic properties and their interaction with the solvent. Calorimetric measurement techniques with probe absorbents, in-situ FT-IR, potentiometric titration and solid-state NMR have been used to characterize the acidic strength these materials. However, these techniques do not necessarily reflect the catalyst performance in the condensed phase reaction environment. Especially in aqueous reactions, their behavior may deviate significantly from what is predicted by one-to-one interaction with probe molecules. In the work to be presented, experimental acid strength measurements are combined with quantum chemical calculations to investigate the interaction of functional groups with water. Organic functional groups of various acidic strengths, e.g. arenesulfonic, propylsulfonic, ethylphosphonic, butylcarboxylic, are incorporated into a SBA-15 structure via co-condensation and tested for their acidic strength in water by potentiometric titration. Additionally, the interaction of these functional groups with water is modeled using an EFP / DFT combined method. The method accounts for two characteristics of the solvent; as a continuum with the other solvent molecules and as one-to-one interactions with the functional group. Determining the bond elongations on the optimized structures, the relative acidic strengths can be predicted. By comparing these results to other experimental techniques, results will be presented for acid strength of the materials in an aqueous reaction environment as well as the role of the water interaction.