This study was carried out in order to investigate mainly the populations of different microorganisms attached to the sand grain surfaces in the slow sand filter beds at Ashford Common Water-treatment works in London area, U.K. using the mechanical shaking technique. It was proved that this technique is one of the more suitable and safe means in extracting microorganisms attached to particles such as sand grains and/or clay particles by applying the scanning electron microscope technique. The scanning micrographs illustrate that there is a direct proportional declination for the numerical densities of the microorganisms at different depths and various time intervals of shaking, while illumination intensities showed a conspicuous pattern particularly in case of complete shading. Simultaneously, It was too difficult to have any other organisms particularly protozoa in the same micrographs which might be referred to the exaggerated abundance of the algal layer "Schmutsdecke", the presence of certain predators (rotifers, chironomid and insect larvae)  and the presence of a very weak  attachment between protozoa and sand grains.