A thin-film-composite hollow-fiber membrane includes a phase-inversion layer, which is in the form of a hollow fiber, and an active layer coated on the phase-inversion layer. The active layer selectively allows passage of water molecules but rejects at least some dissolved ions. The thin-film-composite hollow-fiber membrane can have an internal burst pressure of at least 4 MPa. In a method for forming the membrane, the polymer concentration in the spinning dope from which the hollow-fiber substrate is formed can have a polymer concentration no greater than 5% below the critical concentration.