Water moves in a cycle. The smallest water particles fall out of the clouds as rain. On Earth, they gather in lakes and rivers and flow back into the sea. There it evaporates when the sun shines on it. This causes the water to rise again. It is then invisible fine. In the sky, the water collects again in clouds.
The driving force behind the water cycle is the sun. Due to their warmth, the water evaporates over the sea and the lakes. But even forests are so damp that the water evaporates from them. However, when people cut down large forests, they also reduce the water cycle.
In this cycle, the water is cleaned by nature. Most raindrops fall on land and seep away there. Gravel and earth act like a filter. The place where the water comes out of the ground is called a spring.
How do humans use the water cycle?
The most important thing for all living things is that they always have clean water to drink. No living thing can survive without water. Fish can only live in clean water. Amphibians such as frogs and toads have to lay their eggs in the water so that young animals can develop from them.
Humans need water not only for drinking, cooking, and for washing. More than a thousand years ago, people built water wheels and used them to drive mills. This was easier and more pleasant than doing the work by hand or with animals.
Today, people use the water cycle to generate electrical energy: reservoirs are being built in the mountains. The water then shoots down the valley through tubes onto the turbines. These are connected to generators. They generate electricity.
River power plants are below. The water doesn’t fall that deep, but there is a lot of water. Here, too, electricity is generated with turbines and generators.
These two types are called renewable energy. The sun ensures that the water currents are constantly renewed. People can use it to generate electricity quite easily and cheaply.
Does water always stay clean?
Spring water is very clean and therefore drinking water. However, humans and animals release a lot of dirt into the rivers. Human and animal feces and urine can turn tiny creatures back into useful substances. Nature intended it that way.
What comes from nature does not cause any difficulties for nature. It is different from waste from chemicals and industry. Gasoline, oil, and similar liquids also do not belong there, nor do residues of medication. Nature does not break down these substances, but rather washes them into the sea.
These substances accumulate in the sea. They can kill fish and other creatures. But there are also toxins that accumulate in the fish and mussels. These are mostly heavy metals. When humans eat such fish, they also take in heavy metals.
Man counters this problem with systems for cleaning the wastewater, the sewage treatment plants: Huge filters made of sand and gravel, but also tiny creatures clean the water there. On the one hand, these cleaning systems are becoming more and more effective. On the other hand, there are more and more toxins escaping into nature.