The great increase of population tends to increase the demand of fresh water for humans, animals, and agriculture. For this purpose, a modified solar distiller using flat plate solar collector with gravity assisted heat pipes was design and constructed in Faculty of Engineering, Menoufia University, Egypt, Latitude 30.565o N and longitude 31.013o E. An experimental program was conducted in two ways simultaneously. The first; two conventional distillers with a basin having water depths of 2 and 9 cm. The second, one modified solar distiller with 9 cm water depth using flat plate solar collector with gravity assisted heat pipes. The results obtained indicated that the daily productivities for conventional solar distillers with water basin depths of 2 and 9 cm are 1.48667 and 1.67333 lit/m2, respectively. Also, the daily productivity for the modified distiller with water basin depth of 9 cm is 1.75333 lit/m2. The enhancements in daily productivity of conventional distiller and modified one with 9 cm compared to conventional distiller with 2 cm water depth are 12.55% and 17.93%, respectively. A CFD modeling of transient mode for two conventional distillers with 2 and 9 cm water basin depth was performed. The differences between experimental and CFD results show that the daily average difference percentage between the simulated and experimental absorber plate temperature related to the experimental results was 11.74%, for glass cover temperature was 7.53% and for the hourly productivity was 9% for basin water depth 2 cm and 30.9 for 9 cm basin water depth.