Another variation on a green building is known as "vertical farming." This is a new concept to build high-rise farms (i.e. food grown in specially designed high-rise buildings) so as to reduce the transportation costs of bring food from the countryside to cities. In the proposed building shown above, wind turbines are installed on top of the building to provide energy for the building. Instead of growing the plants in soil, the proposal is to grown the plants using aeroponics. This is an approach where plants are hung in the air and a fine spray containing water and nutrients is sprayed on the roots of the hanging plants. The proposal is to collect rainwater and to store it in water tanks to supply the water. After spraying the roots of the plants, the excess water is then collected and re-used.