A three dimensional numerical simulation of fluid flow in a manifold-laterals system was carried out; several geometrical changes were made to study the effect on water flowing inside the manifold. The manifold hydraulic diameter and the length were kept constant in the study. The geometrical changes include the distance between laterals, the length of the laterals, and the laterals size. It is found that for Reynolds
Number (100 and 1000), increasing the length of the laterals gives uniform flow profile at laterals outlet. Also reducing lateral size will create a similar effect. A good agreement was found between the present and FLUENT6.2 results for mass flow rate from laterals.