For the isolated eb-MBE(2), the error per water molecule increases up to eight water molecules, where it reaches its maximum of 53 kJ/mol. For larger clusters, it decreases and drops to 23 kJ/mol for the largest considered cluster with 20 water molecules. Over all clusters, the mean error per water molecule amounts to 33 kJ/mol. These results are very similar to those reported in Ref. for the same molecular structures, but with The MBEs have been performed using calculations of the isolated subsystems ("iso"), using point-charge embedding ("PC"), as well as using frozen-density embedding with the unrelaxed frozen densities of the isolated fragments ("FDE") and with the relaxed frozen density obtained using freeze-and-thaw cycles ("FDE-ft"). For the isolated db-MBEs, the errors are reduced compared to the isolated eb-MBE(2), but remain rather large. Thus, while for water clusters already the isolated db-MBE could reduce the error per fragment below the threshold of chemical accuracy , for ion-water clusters the use of a suitable embedding potential is essential. As soon as some embedding potential is included, the accuracy of the db-MBE improves. For the db-MBE(1), which only requires calculations for the monomers, the mean error amounts to ca. Overall, we find that for Ca 2+ -water clusters, the accuracy of the embedded db-MBE previously observed for neat water clusters is retained and the mean error in the total interaction energies per water molecule remains below the threshold of chemical accuracy. With relaxed FDE-ft embedding, it is significantly below this threshold. For the Ca 2+ -water clusters the proper inclusion of an embedding potential is crucial, and the best results are obtained with the parameter-free, relaxed FDE-ft embedding potential.