NOVELTY - Transporting water in a fuel cell system comprises transporting water from the first gaseous stream into the second gaseous stream through a non-hydrophilic membrane having a selective layer with an average pore size smaller than 100 Angstrom, wherein the membrane has a water uptake of less than 10% by weight measured at a water activity of 1.0 at 30degreesC at a minimum pure component pressure-normalized water flux of 100 gas permeation unit at 50degreesC.    USE - For transporting water in a fuel cell system, preferably for concurrently heating and humidifying an oxidant stream or an anode side reactant (fuel) gas stream to a proton exchange membrane (PEM) (claimed).    ADVANTAGE - The assembly humidifies the oxidant gas and simultaneously recovers the heat energy in the exhaust gas which contains water, using a stable highly water-selective membrane having a performance that does not suffer physical and chemical deterioration due to heat and moisture despite cycling through a large number of cycles.    DETAILED DESCRIPTION - Transporting water in a fuel cell system from a first predominantly gaseous stream having a higher partial-pressure of water to a second predominantly gaseous stream having a lower partial pressure of water comprises mass and heat transfer through membranes in a membrane module. The first and second gaseous streams flow through first and second zones respectively separated by the membranes in the module. Water is transported from the first gaseous stream into the second gaseous stream through a non-hydrophilic membrane having a selective layer with an average pore size smaller than 100 Angstrom. The membrane has a water uptake of less than 10% by weight measured at a water activity of 1.0 at 30degreesC at a minimum pure component pressure-normalized water flux of 100 gas permeation unit (GPU) at 50degreesC. An ideal selectivity of water is maintained over any other component in either stream greater than 5 at 50degreesC while maintaining a higher partial pressure of water in the first gaseous stream than in the second gaseous stream. A pressure drop is maintained through a selected zone of less than 15% of the absolute pressure at the entrance of the selected zone.    DESCRIPTION OF DRAWING(S) - The figure shows a system in which a PEM cell stack and a water and heat-recovery membrane module are used in combination.    Hot hydrogen-rich gas (21)    Air stream (23)    Exhaust (25)    Hydrogen-depleted stream (26)    Membrane module (30)    Relatively dry air (31)    Humidified and heated air stream (35)    Oxygen-depleted stream (36)