The Ebb and Flow System or Flood and Drain System, works by temporarily flooding a tray and then draining it immediately afterwords.

This operation is conducted by using a pump, controlled by a timer, which makes it an Active Hydroponic System.

The solution is drawn out of a container by a pump, led to the bench or tray where the crops are being cultivated, and once the pumping has ceased, it returns to the container usually by draining through the same pump.

The timer is calibrated to repeat this cycle various times a day às necessary, according to the type of plant, its size, temperature and humidity and the type of growing medium being used, as may be the case.

The growing bench or tray can be made in two ways.

In the first case, one uses a platform fixed to the edges of the bench on which the plants are anchored, and where the  root system remains suspended in air, where only the roots’ extremities are dipped in a thin film of solution left permanently inside that tray.

Today, this setup is outdated, although many still use it.

The second and more common case consists of filling the tray or culture bench with a growing medium in which one anchors the plants' roots.

The growing medium must be biologically sterile and not decomposable, and the most commonly used is composed of volcanic gravel, or river volcanic rolling stones.