This article discusses water and the water cycle for kids in an easy to understand manner. Water cycle experiments that kids can carry out at home are also available on our other page.

Water is a transparent liquid that is found on Earth. It is the most common liquid on the planet. You can find water in seas, rivers, lakes and other water bodies. All living things need it in order to survive.

## Water and its different states

Water can exist in three different states – solid, liquid, and gas. Ice is water in the solid state and water vapor and steam are water in the gas state. Water changes from one state to another when it loses or gains heat and these changes in state occur during the water cycle.

### What are the processes that cause a change in state?

Freezing
Freezing is the process of water changing from its liquid form to its solid form through heat loss. When water loses heat, its temperature falls. At 0°C, it changes into ice.

Melting
Melting is the process of water changing from its solid form to its liquid form through heat gain. The melting point of ice is 0°C. When ice gains heat, it melts and turns into water.

A lot of people misunderstand that because the temperature of ice remains the same when it is melting, it is not gaining any heat. This statement is false. When ice melts, it is actually gaining heat. However, the temperature does not change because the heat is used to help the particles found in the ice to break away from each other. Therefore, the temperature of a melting ice remains the same until all the ice turns into water.

Condensation
Condensation is the process of water changing from its gaseous form to its liquid form through heat loss. Amazingly, it can occur at any temperature below boiling point! This means that water vapor or steam will change into tiny water droplets at any temperature that is lower than 100°C

When you boil water in a kettle, you often see “white smoke” coming out from it. Many people mistakenly think it is steam, but it is actually made up of many tiny water droplets that have condensed when they come into contact with the cooler air. Steam is a colorless gas and cannot be seen.

Boiling
Boiling is the process of water changing from its liquid form to its gaseous form through heat gain. Water reaches its boiling point at 100°C. This means that it will change into steam at this temperature.

Evaporation
Evaporation is also the process of water changing from its liquid state to its gaseous state through heat loss. The difference between evaporation and boiling is that evaporation can occur any time and at any temperature that is above freezing or melting point and below boiling point. When water evaporates, it gains heat from its surroundings and therefore causing the surroundings to lose heat and cooling to be experienced.

A good example of evaporation is when you prespire. After the prespiration evaporates, you feel cooler because the prespiration it gains heat from your body (i.e.: your body loses heat to the prespiration) when it evaporates.

The rate of evaporation is affected by four factors: the temperature, presence of wind, area of the surface that is exposed to the air, and the humidity or amount of water vapor in the air.

## How do these four factors affect the rate of evaporation?

Temperature: when the temperature of the water and the surrounding air is higher, the rate of evaporation will be faster.

Presence of wind: when water evaporates, the water vapor that is formed usually collects just above the surface of the water. When the wind blows, it moves the water vapor away and allows space for more water vapor to form. This means that the stronger the presence of wind, the higher the rate of evaporation.

Area of exposed surface: the area of exposed surface is the area of the water which is exposed to the air. Water vapor goes into the air from this so the greater the area of the exposed surface, the quicker the rate of evaporation.

Humidity: the humidity of the air is the measure of the amount of water vapor in the air. On a dry or less humid day, there is less water vapor in the air and easier for evaporation to occur. On the other hand, humid days have a high amount of water vapor in the air so it is more difficult for evaporation to occur. This also relates back to the presence of wind. When the wind blows, it takes away the water vapor present in the surrounding air and makes the area dryer, allowing more evaporation to occur.

## The Water CycleCredit: By USGS [Public domain], via Wikimedia Commons

The water cycle is a repeated movement of water from the Earth going to the sky and coming back down onto Earth again. It is able to occur as water is interchangeable between the three states of matter. Heat energy from the Sun allows water on the Earth to evaporate and form water vapor, which will allow it to rise into the sky. As the vapor rises up into the sky, it cools and then condenses into many tiny water droplets. These tiny droplets will then gather to form clouds. When the droplets become really heavy and big, they fall from the clouds (precipitation) as either rain, snow, or hail. Rain falls onto our planet as fresh water, and some of them fall onto the ground and then into rivers, lakes and many other water bodies.

## Did you know?

• Water makes up about 75% of the human body and is used to help us carry out life processes such as digestion and respiration.
• Water also helps plants to germinate and photosynthesize to make their own food.
• Although the Earth is made up of about 75% water, only about 1% of that is suitable for drinking. The water cycle helps ensure that we get a constant supply of fresh drinking water.
• When rain falls, it actually helps to purify the air by removing the impurities present in the air such as harmful chemicals and gases.

Our other Science for kids articles:
Plant and Animal Cells for Kids
Magnets and Magnetism for Kids
Heat Energy for Kids