A humidification-dehumidification water purification system and method is disclosed. The system comprises a plurality of evaporator/condenser units and heat exchanger, preferably a solar collector. Contaminated water flows through successive condenser stages to the heat exchanger, and from there through successive evaporator stages. A flow of air is directed through successive evaporator stages in the direction opposite to the flow of water, where it is humidified by water vapor evaporating from the water. The humidified air passes through the successive condenser stages, where it is cooled, thereby condensing pure water and dehumidifying the air. The pure water is extracted from the system, and the dehumidified air can be recirculated through the system. In preferred embodiments of the invention, the evaporator/condenser units are stacked beneath the solar collector, and the system is fully portable and modular and can be either land- or water borne.