Using a new "bottom-up" screening algorithm based on the semi-empirical GFN2-xTB method, we are able to achieve sub-kcal/mol accuracy for water clusters when MBE(n) is paired with an ONIOM-style supersystem correction. This constitutes a predictive level of accuracy by means of which MBE(n) calculations can reliably rank-order the energies of different hydrogenbonding networks, which has proven to be a challenging problem for methods that use single-H 2 O fragments. Numerically-complete four-body results have been presented for (H 2 O) 64 , which represents a reasonable size for the periodic cell in a liquid water simulation. We believe these to be the largest complete application of MBE(4) to date.