What is Water?

Can you think of anything that has no taste, color or smell, comes in the form of a liquid, solid and gas, and is necessary for the survival of people, plants and animals? You guessed it — water! Water is remarkable. You can't taste it, smell it, and you can almost see right through it. It is the only thing on earth that can exist naturally as a solid, a liquid and a gas. Liquid water is found in rivers, lakes and oceans. Solid water is water that is frozen, like snow and ice. Water is a gas when it is in the air of our atmosphere as vapor or steam.

Water is known in science as H₂0. That means the smallest possible amount of water, one molecule, is made from two hydrogen atoms that attach to one oxygen atom. The hydrogen atoms have a positive electrical charge and the oxygen atom has a negative charge. Because opposite charges attract, the charges on either end of the water molecule attract other water molecules and group together, forming water drops. The charges act like magnets. That is how water sticks together in raindrops, rivers, oceans, ponds, and your drinking glass.

Earth is a watery place, unlike most other planets in our solar system. Water covers over 70 percent of the earth's surface. It's everywhere — not only on the surface, but also underground and in the atmosphere. Out of all the water on earth, 97 percent is salt water, like oceans. That means only three percent of all the water on earth is fresh water. Of the three percent fresh water, two percent is solid — frozen in icecaps and glaciers. Out of all the water on earth, only one percent is drinkable, and half of this drinkable water is found below the earth's surface. So, even though Earth is a watery planet, the amount of water we can use is limited.

Water found on the surface of the earth in lakes, rivers and oceans is called surface water. Fresh surface water accounts for nearly half the supply of drinking water in the U.S. (Source: According to the U.S. EPA 1/2 the country depends on ground water for drinking water).

The ground soaks up water like a sponge. The soaked-up water is called ground water. It fills the spaces around sand, gravel and rock below the earth's surface. Sometimes, it moves slowly, and some of it has been underground for thousands of years. These underground streams are created when precipitation such as rain and melted snow seeps into the earth. Ground water can come to the surface in rivers or natural springs. Because of the underground water supply, some rivers, streams, ponds and lakes can remain full even when it doesn't rain or snow.

The other half of our drinking water comes from groundwater sources such as these. We draw the water up to the surface through wells, or use it as it comes to the surface on its own, in springs. Do you know where your drinking water comes from?

All the water we have on earth is all the water we will ever have—we cannot make more. That means it is a non-renewable resource. If we are not careful with water, some day we might run out of clean, fresh water. (For more about renewable and non-renewable resources, see the energy section of RMI for kids.)

Luckily, the water cycle has recycled the water supply for billions of years. We use the same water that the dinosaurs used. That's old! Thanks to the water cycle, our limited supply of water has lasted.

Heat energy from the sun causes water in oceans, lakes and rivers to warm up and turn from a liquid into a gas. This part of the water cycle is called evaporation. Without evaporation, there would be no water in the atmosphere to form clouds.

Condensation occurs after water evaporates into the atmosphere. Water cools in the air, and changes back into tiny droplets of liquid water. Millions of these droplets form clouds. So condensation happens when water changes from a gas to a liquid. This change can be seen in the formation of clouds, or when steam collects on the lid of a pot and forms droplets.

When conditions are just right in the atmosphere, water eventually falls from the clouds in a liquid or solid state. The water that falls, whether it's rain or snow or hail, is called precipitation.

Percolation happens when liquid water seeps into the earth's surface. Percolation helps replenish ground water supplies and provides water for plants. Runoff is the precipitation that doesn't seep into the earth, but flows over land in streams, rivers, lakes and wetlands.