A humidification-dehumidification (HD) solar desalination unit was designed. It seems to be suitable to provide drinking water for population or remote arid areas. Solar water and solar air collectors were designed to provide the hot water and air to the desalination chamber. The desalination chamber was divided into humidifier and dehumidifier towers. The circulation of air in the two towers was maintained by the forced convection. Theoretical and experimental works were done at different environmental conditions. A mathematical model was formulated, in which the thermodynamic relations were used to study the flow, heat and mass transfer inside the humidifier and dehumidifier. Such a technique was performed in order to increase the unit performance. Heat and mass balance was done and a set of governing equations was solved using the finite difference technique. The solar intensity was measured along the working day during the summer and winter months and a comparison between the theoretical and experimental results were performed. The average accumulative productivity of the system in November, December and January was ranged between 2 to 3.5 kg / m² day while the average summer productivity was found between 6 to 8 kg/m² day in June and 7.26 to 11 kg/m² day in July and August.