Abstract: A membrane distillation module comprises a hollow fiber membrane bundle in a housing. A plurality of hydrophobic hollow fiber membranes is secured at each end in membrane boots by chemical bonding of the fiber membrane to a potting compound. The membrane bundle is supported by supporting rods secured to flanges attached to the membrane boots. Fiber packing density is selected to optimize passage of vapor away from the permeate side of the hollow fiber membranes. A center core spanning the length of the membrane bundle serves to conduct feedwater entering the bottom of the module to a bundle top cap where the feedwater is evenly distributed into the hollow fiber membranes. The housing is configured to accommodate expansion of liquid water to the vapor phase during vacuum membrane distillation and to facilitate exit of water vapor from the module via an outlet connected to a vacuum pump.