Why do my plants need so much water?
(Lansing State Journal, September 21, 1994)
And plants transpire. Transpiration is when plants exchange water for carbon dioxide. All leaves have microscopic openings, called stomata. When open, water evaporates out. Carbon dioxide, which plants need to make food, can also diffuse in through the open holes. When the pores close, little carbon dioxide or water enters or leaves the plant. The plant balances the opening and closing of the stomata to acquire enough carbon dioxide and not lose too much water, so it can stay alive.
How much water plants use depends on its type, how much light it gets, and how old it is. A mature house plant can transpire its body weight every day. If people needed that much water, an adult would drink 20 gallons of water a day. In fact, people drink less than one gallon of liquids per day.