Non-drained geokit The non-drained sand filter Geokit is a kit that includes an anti-contamination geotextile, and a filtration grid. A "lateral watertight" Geokit that includes a lateral LEPD film is also available. The non-drained sand filter is mainly made of layers of sand and gravels. The purification process is occurs thanks to the sand and microorganisms lying around grains. Effluents are later returned to the natural environment.