Water is one of the most essential ingredients to life as we know it. Since life on Earth began in water some 3.5 billion years ago, living organisms have evolved an amazing variety of techniques for surviving different watery conditions—from the deepest oceans to the driest deserts. Almost everywhere on Earth, animals and plants use water of all sorts, salty or fresh, hot or cold, abundant or scarce.
Humans are about 60% water by weight—though the percentage is slightly higher on average for men than for women and fairly higher for youth than for the elderly. To replenish our body’s water supply, a typical man needs about one gallon each day (3.7 liters), while a woman needs about 0.7 gallons (2.7 liters).
Can you survive without drinking any water at all? Kangaroo rats have super-efficient kidneys that are so good at recycling water that they get all they need from just the food they eat. Humans, however, need water to survive.
The Texas horned lizard collects and stores drinking water in channels between the scales on its back.
Albatrosses have evolved a way to drink seawater, which is too salty for most birds and land animals. To get rid of excess salt from the water and food they ingest, albatrosses have glands just behind their eye sockets that absorb salt. The glands then excrete a concentrated salt solution that drains out a duct and off the tip of the beak.
No bigger than a speck, tiny eight-legged creatures called tardigrades live either in ocean or freshwater habitats. If drought strikes, they essentially shut down their metabolism and shrivel up into a ball called a tun, waiting until water returns.