Growing lettuce on water in a greenhouse is a method that is commonly used. Foil trays are used for this, into which water is added; the lettuce can grow on this, from shoot to crop without the need to use a solid base or substrate.

A well-designed foil tray can be installed in just a few steps. A protective geotextile is applied first to the bottom of the tray, after which watertight foil is applied. Side ducts are fitted into the side of the tray for the water supply and drain ducts are installed in the base for drainage. The foil structure can be secured around the tray using stainless steel strips.