Monohydrated and dihydrated calcium oxalates have been widely studied in the literature because of their role in urolithiasis, a mammal pathology responsible for the formation of stones in the kidney. It is clear that the physicochemical environment plays a crucial role in the crystal growth and the resulting morphologies of calcium oxalates. To study these processes, reliable models for the calcium oxalates’ faces, exposed to water and potential additives, are needed. Here, we have used a total surface energy minimization approach to predict the crystal morphology of the calcium oxalate monohydrate and dihydrate phases. Surface energies were calculated at density functional theory level, taking into account surface relaxation and the effect of solvation. An excellent agreement was found between theoretically predicted morphologies and their experimental counterparts obtained by SEM, clearly demonstrating the importance of the inclusion of water in the model for the prediction of morphologies.