Water

Water is all around us.

It is in the big blue sea. It is in the rain. It is also in the air.

Water can change its shape. It can be a liquid. It can be a hard solid called ice. It can even be a gas called steam.

Water is very special. It can dissolve many things. This helps it move bits of food to living things. It is vital for all life.

Most of the water on Earth is in the ocean.

Some water is in big ice caps. A little bit is in the ground.

We use water for many things. We use it for farming. We use it for washing and cooking. It is a part of our world.

Water is a special substance called H2O.

It has no taste and no smell. It is clear, but it can look blue. Water covers about 71% of the Earth.

Most of this water is in the oceans. Only a small part is fresh water. Humans use much of this for farming. We also use it for washing and cooking.

Water can change its form. It can be a liquid. It can be a solid called ice. It can also be a gas called steam or water vapor.

Adding or taking away heat causes these changes. For example, ice melts into water when it gets warm. Water turns into vapor when it boils.

Water is also called a "universal solvent." This means it can dissolve many things. It can dissolve more substances than any other liquid. This helps move bits of food to living things. This makes water vital for all life on Earth.

Water is a very special substance known as H2O.

It is a clear liquid that has no taste and no smell. You might notice it looks a little bit blue. Water is the main part of our oceans, lakes, and streams. It is also found inside every living thing on Earth. Scientists call it the "universal solvent." This means it can dissolve more substances than any other liquid. This amazing ability helps it carry important things to living things.

Water can change its form depending on how much heat it has.

When it is warm, it is a liquid. If you add or remove heat, it changes. Adding heat can turn liquid water into a gas called steam or water vapor. Removing heat can turn liquid water into a solid called ice. If you keep removing heat from vapor, it can turn straight into ice. This is how frost forms on cold surfaces. Water is unique because it can exist as a solid, liquid, and gas all at once on Earth.

Water has some very strange rules about how it behaves.

Most things get heavier and more crowded when they get cold. Water is different because it becomes less dense as it cools. When water freezes into ice, it actually expands by about 9%. This expansion can be strong enough to crack rocks or burst pipes. Because ice is less dense, it floats on top of liquid water. This is very important for life in the winter. The floating ice acts like a blanket to protect living things in the water below.

Our planet is covered in a huge amount of water.

About 71% of the Earth's surface is covered by water. Most of that volume, about 96.5%, is found in the seas and oceans. Only a small amount is found as groundwater or in glaciers. Glaciers in Antarctica and Greenland hold about 1.7% of the water. There is also a tiny amount of water in the air as vapor or clouds. Water moves in a constant cycle through evaporation, condensation, and precipitation.

Humans use water for many important jobs every day.

About 70% of the fresh water we use goes to agriculture to grow food. Fishing in the water provides 6.5% of the protein for people around the world. We also use water to move large items like oil and gas on big boats. In our homes and factories, we use water, ice, and steam for heating and cooling. It is also very useful for cooking and washing. Many people enjoy water for fun through sports like swimming, surfing, or skiing.

Water is an inorganic compound with the chemical formula H2O.

It is a transparent, tasteless, and odorless substance. Most pure water appears nearly colorless, though it can have a slight blue tint. Water is the primary component of Earth's oceans, lakes, and streams. It is also the main fluid found within all known living organisms. Because it can dissolve more substances than any other liquid, scientists often call it the "universal solvent." This ability is vital because water carries many dissolved minerals and nutrients to living things.

The unique behavior of water comes from its molecular structure. Water is a polar molecule, meaning it has a positive end and a negative end. This polarity allows for strong intermolecular hydrogen bonding.

These bonds act like tiny magnets between molecules. This specific chemical structure is a major contributor to all of water's physical and chemical properties. It also allows water to act as the "solvent of life" in nature. Most natural water includes various dissolved substances rather than being chemically pure.

Water is unique because it exists in three states on Earth: solid, liquid, and gas.

The solid state is known as ice. The liquid state is simply water. The gaseous state is called water vapor or steam. These states change through phase transitions driven by the addition or removal of heat. Freezing turns liquid to ice, while melting turns ice to liquid. Vaporization turns liquid to vapor, and condensation turns vapor back to liquid. You can also see sublimation, where ice turns directly into vapor, or deposition, where vapor turns directly into ice.

One of the most surprising things about water is its density.

Most substances become denser and more crowded as they cool down. Water behaves differently. It reaches its maximum density at 3.98 °C (39.16 °F). As it cools further toward the freezing point of 0 °C (32 °F), it actually begins to expand and become less dense. When it freezes into ice, it expands by about 9%. This expansion can create enough pressure to burst metal pipes or crack solid rocks. Because ice is less dense than liquid water, it floats on the surface. This allows ice to insulate the liquid water below, protecting aquatic life during freezing winters.

Water's behavior also changes depending on the surrounding pressure.

At sea level, water freezes at 0 °C and boils at 100 °C. However, if you go to a high altitude, the atmospheric pressure decreases. This causes the boiling point to drop by 1 °C for every 274 meters of elevation. In the deep ocean or underground, high pressure allows water to remain liquid even at very high temperatures. For example, temperatures in the Old Faithful geyser exceed 205 °C (401 °F). At hydrothermal vents, temperatures can even exceed 400 °C (752 °F).

There are specific points on a phase diagram that define water's limits. The triple point is a specific temperature and pressure where solid, liquid, and gas all exist at once. This occurs at 273.16 K (0.01 °C) and 611.657 pascals. There is also a critical point at 647.096 K (373.946 °C). Beyond this point, water becomes a supercritical fluid. In this state, it has properties of both a liquid and a gas. This fluid can be used in industrial chemistry or helps minerals form in the Earth's mantle.

Water covers about 71% of the Earth's surface.

Most of this volume, about 96.5%, is held in the seas and oceans. The rest is distributed in different ways. Groundwater makes up 1.7% of the water. Glaciers and ice caps in Antarctica and Greenland hold another 1.7%. Only a tiny amount, 0.001%, exists in the air as vapor, clouds, or precipitation. This water moves constantly through the water cycle. This cycle includes evaporation, transpiration, condensation, precipitation, and runoff, which eventually leads back to the sea.

Humanity relies heavily on water for the global economy. Approximately 70% of the fresh water used by humans is dedicated to agriculture. Fishing is also a major industry, providing 6.5% of the world's protein. Beyond food, water is essential for transportation. Many commodities like oil and natural gas are moved by boats through canals and rivers. In industry and homes, water, ice, and steam are used for heating and cooling. It is also used for cooking, washing, and many popular sports like swimming and skiing.