G4 – The Water Cycle 700 – 800L_03

These droplets fall towards the earth when they become too heavy for the wind currents to hold them aloft. When water falls from clouds, it is called precipitation.

The water falls as rain if the air is warm. If the air is cold, the water may freeze and fall as snow, sleet, or hail. Most precipitation falls into the oceans. Some falls on land.

Once on the ground, water’s journey through the water cycle continues. Some of the water that falls to the ground may run across Earth’s surface. This process is called runoff as the liquid water travels to rivers, lakes, or oceans. Runoff may pick up fertilizer and other pollutants and deliver them to the water body where it ends up. When this happens, runoff may pollute bodies of water. Water can also seep into the ground in a process called infiltration. Some of the water may seep deep underground. Some may stay in the soil, where plants can absorb it through their roots. Underground water is a common source of drinking water.

The image below illustrates what the water cycle looks like on Earth. In the image, it looks like the water cycle occurs mostly over land. That is far from reality. In fact, most of the water that is recycled never reaches land. Why do you think this is? Here’s a hint: most of Earth is covered by water. Oceans cover about two thirds of Earth’s surface. As a result, most evaporation occurs in oceans and most precipitation falls back into the ocean.

The water cycle is continuous cycle. It has no beginning or end. Most of the water you drink may be billions of years old. You now know it’s okay to drink. The water has been through a recycling process. That’s good news when you think about where this water has been. The water you are drinking may have once quenched the thirst of a dinosaur.