Water and the water cycle
What is water and what is the water cycle?
Water is vital for all living things. Animals drink water, while plants take water up through their roots in a process called osmosis.
Water never leaves the Earth, it simply moves around the ‘water cycle’. The water cycle follows the journey of water from oceans to clouds to rain to streams to rivers and back into the ocean. The water cycle involves the scientific processes of evaporation and condensation and is also known as the hydrologic cycle ('hydro’ means water in Greek).
Top 10 facts
- Humans are made up of about 75% water.
- Water can exist in three forms: liquid (water), solid (ice) or gas (water vapour).
- 2/3rds water in polar ice caps.
- 97% of water is in the oceans (this is salty water) and 2% is in the ice caps, leaving only 1% available for us to drink.
- About 70% Earth is covered in water.
- There are underground reservoirs called aquifers.
- Some water in the ground may stay there for thousands of years.
- You might be drinking water that dinosaurs drank! Because water is recycled and doesn’t leave the Earth or is formed all the water currently on our planet is the same water that has been there for millions of years.
- The Nile is 4132 mile long, making it the longest river in the world.
- Water can be used to create electricity through a hydro-electric power station
Did you know?
- Water leaving your body as urine or sweat is evaporated and recycled through the water cycle. The water in your wee and sweat is returned to the water cycle, while other parts (urea and salt for example) are left behind as they do not evaporate with the water.
- Beneath the ground is a water table. This is the level that the ground is saturated with water and can rise or fall depending on the amount of rain that falls.
- When the ground becomes saturated with water it can cause flooding. The water that falls as rain no longer has anywhere to go as the ground is full of water so it stays on top. Many rivers and streams swell with water when this happens and can break their banks and flood as well.
- Frozen water can move and carve out valleys in the form of glaciers. Some of the ice in glaciers has been there for thousands of years and will only re-enter the water cycle is the ice melts.
- Hydroelectric power stations use the force of falling water to generate electricity. They are formed of a reservoir that is high up in a mountainous area, with the generators down below. Water is released and the kinetic energy in it is transformed into electrical energy.
- The longest someone can survive without water is about three days. We need water for lots of jobs in our bodies, such as digesting food. Water is also found in our immune systems and makes up a large part of our blood. Without water our bodies would stop working.
- Drinking water needs to be clean to prevent people from getting diseases. In the UK we have water treatment plants that remove all of the pollutants in water before it can become drinking water. The water has chemicals added to it and is filtered. Formal water treatments to create drinking water have only really been around for the past 100 years or so.
Look through the gallery below and see if you can spot the following:
- Water cycle diagram
- Types of precipitation
- Run off
- Water evaporating from a lake
- A droplet falling into water
- Antarctic ice sheet
- A glacier entering the sea
- A glacier in a valley
- Glass of water
- River Nile
- A stream
- A water treatment plant
Water is vital for life and humans need to drink it regularly to make sure we have enough in our bodies. When we don’t have enough water in our bodies it is called dehydration.
There are many places that water can be found. We call these ‘bodies of water’. Bodies of water include: oceans, seas, streams, rivers, lakes, ponds, wetlands, marshes, bays, harbours, coves, deltas, and even puddles! There are generally considered to be five main oceans: Pacific, Atlantic, Indian, Southern and Arctic.
Water is never created or destroyed; it simply journeys through the water cycle being recycled each time. The water that we use today has been around for millions of years.
The water cycle takes water on a journey and is made up of six possible processes: condensation, infiltration, runoff, evaporation, precipitation, transpiration.
The heat from the sun causes water to turn into a gas known as water vapour. This process is called evaporation. When the sun turns water from plants and trees into water vapour the process is called transpiration.
When water cools down it forms a cloud. This process is called condensation. When a cloud becomes too heavy the water falls to the ground as precipitation. Precipitation can either take the form of rain, sleet, hail or snow.
When precipitation lands on the ground it seeps into the ground or runs off into drains and water ways. It ends up in streams and rivers and eventually returns to the oceans.
Not all water falls into streams, oceans and rivers. A lot of water is locked up in the polar ice caps.
There is evidence that the polar ice caps are gradually melting due to global warming. This will eventually cause the sea level to rise.
Words to know:
Water vapour – water in a gas form
Ice – water in a solid form
Ice cap – a large area (less than 50, 000km²) that is covered in ice.
Condensation – the process of cooling water that turns it from a gas (water vapour) back into a liquid
Infiltration – when water moves down through the ground
Runoff – when water travels over the top of the ground and back into a stream, river or sea
Evaporation – the process of heating water that turns it from a liquid into a gas (water vapour)
Precipitation – water falling to the ground from a cloud. It can be in the form of rain, sleet, hail or snow.
Transpiration – the process of water evaporating out of the leaf of a plant or tree.
Ocean – a very large area of sea. There are usually considered to be five main oceans (Pacific, Atlantic, Indian, Southern and Artic.
River – A flow of water that leads to the sea. A river is a larger flow of water than a stream.
Stream - A flow of water that usually leads into a river. A stream is a smaller flow of water than a river.
Aquifer – an underground reservoir of water
Reservoir – an area where water is stored
Cloud – condensed water (water vapour) that is visible in the atmosphere
Hydropower – the method of changing the kinetic energy from falling water into electrical energy.
Just for fun...
- Play some wetland games
- Investigate fresh water in an animation video
- An interactive water cycle to watch
- Bathroom science: find out about water-based science
Find out more
- Find out more about all aspects of water, from glaciers to saline water and hydroelectricity
- Watch an animation from the Met Office about water
- Discover how electricity is formed at hydroelectric power stations
- Print out a child-friendly water cycle diagram from the U.S. Geological Survey and the Food and Agriculture Organization of the United Nations
- Download TheSchoolRun's water cycle worksheets: The water cycle, Make your own water cycle and Complete the water cycle
- Watch an animated water cycle
See for yourself
- Watch a video about the journey of water, from rainfall to reservoirs to homes
- Make a mini water cycle in a bowl: step-by-step instructions
- Watch a BBC clip on how water is treated in the UK before it is returned to the water cycle
- Watch an animation of the water cycle