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The hydroponic system of water culture is probably the simplest to set up on a small scale. In this system the plant roots are totally immersed into a solution of nutrients. The main disadvantage to this system is both the large amount of water that is required per plant and also the need to aerate the solution continuously.
The actual design of the system is really only limited by the imagination of the builder. The system must however provide means to
(1) support the plant above the solution,
(2) aerate the nutrient solution,
(3) prevent the light from reaching the solution (this is required to prevent the growth of algae).
A standard tray may be made of concrete or of plastic-lined wood. A typical size would be 6 to 12 inches deep, 2 to 3 feet wide, and as long as is convenient for you. The plants can then be supported by inserting them through holes that are drilled in a plywood top or perhaps through holes punched in a l-inch-thick Styrofoam sheet that floats on the solutions surface.
You can make a small hydroponic system from a child's wading pool, a plastic pail, a fish tank, or even a drinking tumbler. A large tomato plant should really be grown in a container that holds at least 4 liters as a smaller container will be cause the solution to be used up too quickly. Lettuce plants, for example, may be grown in smaller containers.
In a hydro setup using aquaculture, short plants such as lettuce and spinach will generally support themselves. Drill a 1-inch hole in the Styrofoam or wooden cover and then insert a transplant. The plant can be held in place by packing some flexible material such as some cotton into the hole around the stem. A plant that is started in a medium such as sand, perlite, or vermiculite can be transplanted very easily to the water culture because these materials can be washed away from the roots quite readily.
Vining plants such as cucumbers and tomatoes, however, should be supported by string. When pruned to just a single stem they can be gently wrapped around a loosely hung string as they continue to grow.
You should aerate the nutrient solution continuously by pumping air through a perforated hose or through some pipe that is immersed in the solution. For smaller systems, an aquarium pump and porous stone will work just fine. Be sure not to bubble the solution too vigorously as excessive movement may damage the tender roots and effectively impair plant growth.
You should change the nutrient solution every two weeks whilst the plants are small and then once a week when they begin to mature. You should also add water daily to keep the solution at a constant level. | 
