A modified design for a desalination unit using flash evaporation at atmospheric pressure and low temperature is investigated. The evaporation chamber is introduced inside the condensing chamber. An electric heater is used for heating the brackish water. The experimental setup is used to study the effect of temperature and mass flow rate of heating brackish water, flow rate of cooling water and operating time on the productivity, energy consumption and efficiency of the unit. The results show that the performance of the system is strongly affected by the temperature and mass flow rate of water heated. The unit starts to output freshwater after ten minutes of operation and becomes steadly about twenty minutes later. The temperature and mass flow rate of brackish water are 75 ^oC and 4.8 lit/min. The maximum water productivity, system efficiency, energy consumption are 2.95 lit/h, 85 % and 0.82 kWh/kg respectively. The model is expected to be used in solar energy desalination units.