Water conduction and salt rejection through BN NTs embedded in a Si3N4 membrane was investigated by Hilder et al. They find that a BN NT 0.69 nm in diameter embedded in a Si3N4 membrane can, in principle, obtain 100% salt rejection at concentrations of seawater (500 mM) while allowing water to flow at rates as high as 10.7 water molecules per nanosecond. Moreover, ions continue to be rejected at hydrostatic pressures as high as 612 MPa. When the NT diameter is increased above 0.83 nm, ions can enter the tube. By assuming a pore density of 2.5 × 1011 cm−2 and at an operating pressure of 5.5 MPa, Hilder