Where our water comes from and how to keep it clean
Water covers most of Earth’s surface, but most of it is salty sea water. Only a small part is fresh water, found in rivers, lakes, glaciers and underground as groundwater. The water cycle keeps water moving: the Sun’s heat evaporates water from oceans and lakes, plants release water vapour through transpiration, the vapour cools and condenses into clouds, and water returns as rain, snow or hail. Rainwater soaks into the ground and refills groundwater through infiltration.
Water dissolves many substances, so it often contains impurities. Mud and sand can be removed by sedimentation and filtration, and germs are killed by boiling or by adding chlorine. Water treatment plants clean water before it reaches homes. Sewage, factory waste and plastic pollute rivers, harming fish and spreading diseases like cholera. Overuse of groundwater and cutting forests lower the water table, causing shortages.
Why it matters
Clean water is needed for drinking, farming, industry and keeping healthy. Rainwater harvesting, fixing leaking taps and drip irrigation help save water, especially in dry regions. Understanding pollution and purification helps communities protect their rivers and wells. This topic links to solutions, separation methods and environmental science.
Key terms
- Groundwater
- Water stored beneath Earth’s surface in soil and rock layers.
- Transpiration
- The loss of water vapour from plant leaves into the air.
- Water table
- The upper level of groundwater below the ground surface.
- Rainwater harvesting
- Collecting and storing rainwater for later use or to recharge groundwater.