Answer: Transpiration

While we all know plants need water to live (and surely more than a few of us have killed a house plant or two due to a lack of proper watering), what many people don’t realize is that plants are pretty gluttonous when it comes to water consumption. In fact, despite how aggressive most plants are in taking up water through their root systems, typically 3 percent (and sometimes as little as 0.5 percent) of that water is used for actual metabolic processes.

The rest of that water, upwards of 97 percent of it, simply evaporates through the surfaces of the plant (leaves, stems, and flowers) by a process known as transpiration (and guttation at night). This process, analogous but not equivalent to sweating in humans, produces an astounding amount of water vapor. An acre of corn, for example, gives off 3,000-4,000 gallons (11,400-15,100 liters) of water per day and a single large oak tree can transpire 40,000 gallons (151,000 liters) of water a year.

Because such high volumes of water vapor are produced by the plants in tropical areas, it can even affect local weather patterns—in the photo seen here, the sheer amount of water vapor dumped into the atmosphere by the numerous plants in the Amazon rain forest peppers the area with thousands of tiny clouds.