The fouling of high purity water can be quantified by comparing the effect of fluid velocity (laminar and turbulent) on the accumulation of cell on tube surfaces. Direct observations were monitored under light microscope to quantify numbers of the cells sedimented on a of glass slide inserted into the tube. CFD (Computational Fluid Dynamics) software, fluent was used to analyse the problem. Results show the increase of cell count coincided with the increase of the water velocity resulted in increase in the fluid fractional resistance.