The experimental and theoretical studies on the search for the new promising filter materials and nanomaterials with superior permeability and specified selectivity of filtration intensively go ahead in the last decade. Theoretical studies are mainly based on molecular dynamics simulations of filtration and sieving of the fluids, gases and ions through the nanoporous materials of different nature. Layered or quasi-two-dimensional nanomaterials seem to be the most promising for such problems as water desalination, gases and ions separation as well as for DNA sequencing. In the present research the hexagonal boron nitride-based (h-BN) membranes with rectangular nanopores were examined for the first time in order to estimate their potential as water filter material. The nonequilibrium molecular dynamics (NEMD) simulations were performed to get theoretical estimates of ion rejection and water conductance of three model h-BN membranes. We introduced the terms "zigzag" and "armchair" for the first time to characterize the types of rectangular nanopores in two-dimensional materials with hexagonal packing of atoms. The results of NEMD simulations showed that a model membrane with rectangular armchair nanopores of 7.514 Å width has an excellent permeability-selectivity efficiency including 100% salt rejection.