Water > What is Water?

All living things, from tiny cyanobacteria  to giant blue whales , need water to survive. Without water, life as we know it would not exist. And life exists wherever there is water.

All organisms, like animals and plants, use water: salty or fresh, hot or cold, plenty of water or almost no water at all. They are adapted to all kinds of habitats , from sizzling deserts to the freezing, pitch-dark ocean floor. The first living things appeared in the ocean nearly four billion years ago. Some, like our ancestors, adapted to life on land. Humans have figured out how to survive in swamps, deserts, and all kinds of habitats in between.

The ocean is still home to more kinds of life than anywhere else on the planet.

Water may not seem special. It's clear. It has no taste. It doesn't smell like anything. But if it couldn't do the things it does, life on Earth  would not exist.

Water is a tiny molecule. It consists of three atoms : two of hydrogen and one of oxygen. Water molecules cling to each other because of a force called hydrogen bonding. It's the reason why water can do amazing things.

Water is a shape-shifter. It exists in three states on Earth: liquid, gas, and solid:

• Liquid water is a jumbled bunch of water molecules. It comes out of our faucets, flows underground and in rivers and oceans, and forms clouds and fog in the air. 

• When water molecules escape from liquid water and float into the air, they turn into an invisible gas called water vapor. The spaces between the molecules are much bigger than the molecules themselves.

• When water freezes into a solid, it does a strange thing: it floats! (Most other solids become denser and sink.) As ice forms, water molecules arrange themselves neatly in a crystal structure. The empty spaces between the molecules act as flotation devices — the way a life preserver holds you up.

Liquid water can absorb and store huge amounts of heat without melting, freezing, or boiling. That's why water affects or controls climate in many ways. (Climate is the average weather in a place, over a long time.)

Ocean currents move warm water around the globe. At the North and South poles, sea ice  forms and melts with the seasons. Water vapor in the atmosphere holds in the Sun's  heat like a blanket. Clouds and ice sheets reflect some of that heat back into space. Together, these processes keep our planet from getting too hot or too cold.

The water on Earth today is all the water we will ever have.

The ocean holds most of it — over 97% of Earth's water is salty. Less than 3% is fresh — this is the water we drink, water plants with, and use to make things. Most of the fresh water is locked up in glaciers and ice caps. Only a tiny bit of what's left over is available for humans.

Some places are too wet and others too dry. In fact, half of the world's fresh water can be found in only six countries! More than a billion people live without safe, clean water, and the number of thirsty people is growing.

Water is precious. We can't get more. How do we make sure there is enough clean, fresh water to share with all living things?

Remember that every drop we use — or waste — continues through the water cycle. Stuff we put down the drain ends up in someone — or something — else's water. Chemicals like fertilizers and pesticides pollute lakes and oceans, harming the organisms that live in them.

We need to protect swamps and riverbanks. These wetlands clean water naturally, and provide important habitat for many wild birds, fish, and other species. People are working to restore damaged or lost wetlands.

We can use water more wisely. For example, it takes a lot of energy  to produce bottled water, and not everyone recycles  the plastic bottles. We can use less, too, in simple ways like drinking tap water and turning off the faucet while we brush our teeth.

Together, we can protect fresh water now and for the future.