This paper describes a study to develop the analytical tools and to make preliminary observations needed to help end the debate over the importance of the filter cake that forms on the surface of the sand media and focuses on the sand surface where the biologically active schmutzdecke is located. Some authors suggest that the deeper region of the sand media is where significant adsorption and biodegradation occur and the filter cake is merely an extraneous part of slow sand filtration. Other authors have clearly demonstrated the top three inches of the sand media is where almost all of the purification occurs. These analyses of filter cake characteristics will allow future investigations to identify the mechanisms of removal of influent pathogens, suspended solids and organics under different operating conditions, including influent water temperature, sand characteristics and loading rates.