A seawater greenhouse uses the sun, the sea and the atmosphere to produce fresh water and cool air. The process recreates the natural hydrological cycle within a controlled environment. The front wall of the building is a seawater evaporator. It consists of a honeycomb lattice and faces the prevailing wind. Fans control air movement. Seawater trickles down over the lattice, cooling and humidifying the air passing through into the planting area. Sunlight is filtered through a specially constructed roof. The roof traps infrared heat, while allowing visible light through to promote photosynthesis. This creates optimum growing conditions – cool and humid with high light intensity. Seawater that has been heated in the roof passes through a second evaporator creating hot, saturated air which then flows through a condenser. The condenser is cooled by incoming seawater. The temperature difference causes fresh water to condense out of the air stream. The volume of fresh water is determined by air temperature, relative humidity, solar radiation and the airflow rate. These conditions can be modeled with appropriate meteorological data, enabling the design and process to be optimized for any suitable location.