Plants in hydroponic grow systems of all types depend on a water solution that is rich in the nutrients that are necessary for growth and development because there is no soil to supply the nutrients.
In some systems, the plants are floated on top of grow tanks filled with the solution. An example of this type of grow tank would be the common grade school experiment that suspends a plant right at water level in a glass jar so the children can see the roots grow into the solution over time. Of course, commercial hydroponics tanks are much larger and contain many more plants.
Several other hydroponic system types have the plants slightly separate from the hydroponic reservoirs that hold the nutrient solution. Depending on the type of growing system, the nutrient solution might be dripped into individual pots, streamed past dangling roots, or flooded onto the tray containing the plants and then drained away.