World Water Day takes place every year on 22 March. The purpose is to highlight the importance of clean water and using water sustainably. The theme for 2020 is "Water and Climate Change", because climate change – along with the many other problems it causes – is having a huge effect on water. Because temperatures are rising, more water is evaporating worldwide. In some regions, this means that the risk of flooding is increasing, while other regions that are already very dry are becoming even drier. In both cases, there will be problems with the availability of clean water for people, animals and plants.
Let's build a mini water treatment plant
What happens to the water if a bucket of dirty water is tipped over in the garden? It seeps through the soil, passes through sand and gravel and so gradually becomes cleaner. Deep underground, it meets an impermeable layer. Here, it collects in the spaces: this is the water that we call groundwater.
Here's an experiment to show you how water is cleaned as it travels through the soil.
You will need:
• 4 old flowerpots or 4 plastic cups with a hole in the bottom
• 1 large glass
• Coarse sand
• Fine sand
• 1 coffee filter
• Dirty water
• Washing-up water
And here's what you do!
Fill the containers as shown on the diagram: one with gravel, one with coarse sand and one with fine sand. Stack the containers one on top of another and put the coffee filter in the fourth container. Now put the four containers inside the large glass – and you've made a water treatment plant!
Now gradually pour the dirty water into the first container and watch what happens to the water.
Then repeat the experiment with washing-up water.
Even if the water looks clean afterwards, it must not be drunk! There are still invisible contaminants. The experiment with the washing-up water shows that detergent is not filtered out by the filter. Even though the water at the bottom looks clean, it will start to foam if you shake it!
To mark the 100th anniversary of natur&ëmwelt, we want to cleanse rivers, streams and ponds all over the country for a length of 100 km. You are welcome to come along with your family and help us.
If you would like to join in, please go to our website at