What is deep water culture?
Deep Water Culture (DWC) is a method of growing plants without soil. When using the DWC method, plant roots are kept fully submerged in the nutrient solution (the "water") and the solution is kept oxygenated, usually with an air pump and air stone. The solution can be kept oxygenated in a number of other ways, such as with a fountain (a water pump that circulates the water through the air) or with electrolysis. Keeping the water oxygenated and circulated is vital because if the roots are fully submerged in stagnant water without oxygen, the plant will suffer and in most cases simply die.
Why does the water need to be oxygenated?
Just like animals, plants need oxygen to produce energy from food. Even though plants release oxygen during photosynthesis, the roots get their oxygen from the surrounding dirt and air. While some plants can get by with very stagnant water, even these will thrive better with well-oxygenated water.
Keeping the water circulating and oxygenated also helps prevent algae growth and helps keep harmful bacteria and fungus at bay. One of the first signs your hydroponic plant's roots aren't getting enough oxygen is often the smell and color of bacterial growth.