Backwashing of rapid gravity filters is an important part of the water treatment process, particularly in drinking water treatment. Understanding the mechanisms in the backwash process is fundamental for the design of an effective and efficient backwash system, The development of instrumentation to increase our knowledge of backwashing has shown that combined air and water wash is the most effective method of cleaning the bed, although this may cause operational difficulties requiring a different design of filter, Techniques that have been developed to study backwashing include the use of video cameras and endoscopes with subsequent image analysis, More recently, work has focused on the development of pressure transducers for detecting whether the bed is being subjected to sufficient agitation, e.g. that collapse-pulsing is occurring within the bed, The paper-describes the development of these techniques and the results of laboratory and full-scale research that has employed them.