Why Do Living Organisms Need Water?

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With all living organisms composed of 60 to 90 percent water, all organisms require the substance as a basic building material as well as to regulate internal body temperature, transport nutrients through the bloodstream and flush out wastes. According to the United States Geological Survey, humans and other mammals rely on water to serve as a shock absorber for their brains and spinal cords as well as to lubricate joints.

Human beings are composed of 60 percent water. According to the Journal of Biological Chemistry, the human brain and heart are each 73 percent water while the lungs are approximately 83 percent water. Even human bones are roughly one-third water.

Human beings must consume water daily to thrive. According to Nestle, which sells bottled water, the average adult male requires 3 liters of water per day while the average adult female needs 2.2 liters per day.

The key to water's usefulness to organisms is its surface tension. This tension makes water "sticky," allowing it to transport nutrients through an organism more easily and allowing it to be metabolized for energy. This same surface tension also helps water flush out toxins. Water is also crucial to many life forms that live primarily or completely in water-based habitats.