This invention relates to an asymmetric composite membrane containing a polymeric matrix and carbon nanotubes within a single membrane layer, where the carbon nanotubes are randomly oriented within the polymeric matrix and the composite membrane is formed by phase inversion. This invention also relates to a method for producing the composite membrane which includes: coating a surface with a film of a polymer solution containing a polymeric matrix and carbon nanotubes dissolved in at least one solvent; immersing the coated surface in a non-solvent to affect solvent/non-solvent demixing resulting in phase inversion to form a carbon nanotube-containing membrane; and optionally, removing the carbon nanotube-containing membrane from the surface. The invention also relates to a desalination method using the composite membrane.