In the present work characteristics and performance of a natural vacuum desalination system using low grade heat source is studied numerically and experimentally. In the numerical work, a program to solve the governing equations in forward time step marching technique is developed. In the experimental work a lab scale natural vacuum system using electric heater as a heat source is designed and tested. The surface area of seawater in the evaporator is 0.5 m. The numerical and experimental results show a good agreement. By using numerical simulations effect operating conditions such as heat source temperature, condenser temperature, heating coil surface area, and the present of heat recovery unit are explored. The simulation showed that, the present system with evaporator surface area of 0.2 m², operation time of 9 h and source temperature of 80 °C will produce 6.63 L of fresh water ant thermal efficiency is 70.4%. The main conclusion can be drawn here is that the performance of the natural vacuum desalination system is mainly affected by maximum temperature in evaporator and minimum temperature in condenser. On the other hand, the surface area of heating coil and the heat recovery unit showed only a small effect.