The calculations use the def2-TZVP base set, which means that the largest molecules contain more than 1500 basis functions. Intrinsic Atomic Orbitals (IAO) and Projected Atomic Orbitals (PAO) are employed for orbital localization, with each fragment consisting of the orbitals on a water molecule and the corresponding bath orbitals obtained from the SVD procedure. Six different cut-off thresholds are selected: 0.001, 0.002, 0.005, 0.01, 0.015, and 0.02. The fragments are then solved using the CCSD(T) solver, and the (T) correction is applied after the SCF-DMET/CCSD calculation has converged. The electronic energies calculated with thresholds greater than 0.001 are compared to those calculated with ϵ = 0.001. Table presents the relationship between the number of water molecules, the chosen threshold, and the relative error, expressed in kcal/mol. All calculations in this study were performed on a MacBook Pro equipped with an Apple M3 Pro chip. All calculations converge after three iterations as the matching error drops below the set threshold. It is expected that the calculations involving covalently bound fragments will experience a similar drop in the matching error. According to the table, it is evident that if the threshold is kept constant, the relative error increases as the system size grows. This occurs because the threeindexed electron repulsion integral (ERI), V Q µν , is long-ranged. As a result, its coefficients decay very slowly with the distance between atomic orbitals. Consequently, as the system size increases while maintaining the same threshold, the truncation error also increases. However, it is important to note that the orbital rotation matrix is not long-ranged. This is because it is derived from the singular value decomposition (SVD) of the localized Hartree-Fock density matrix, which decays exponentially with the distance between the centroids of the atomic orbitals. This means that if the system size is large enough, the error term