An evaporation device has an inner tube and an outer tube. The inner tube is made of a hydrophilic membrane, such as DutyionT. The outer tube is preferably made of a material that readily absorbs solar radiation and is a good heat conductor. There is a gap between the inner tube and the outer tube for the flow of air. The inner tube contains a flow of impure water. The hydrophilic membrane allows water to pass to the outside of the inner tube as vapor, but prevents impurities from passing through. Air flowing in the gap takes up the water vapor and humidified air exits the evaporation device. This humidified air is subsequently cooled to collect the vapor and provide purified water, e.g. at a condenser.