Clean Water, Games

Why do castaways die of thirst on the sea?

Today we will realize why castaways at sea die of thirst and why it is important to collect rainwater and save water.

Tell the children that our planet – Earth – is special because it has lots of water. Water creates vast oceans and seas. It flows in rivers. It is absorbed in soil, giving life to trees, flowers and animals. Water is also in the atmosphere. It accumulates in the clouds to fall as rain. Did you know that water covers more than half of the Earth’s surface? (On a board or on a piece of paper draw a circle symbolizing Earth and color about 70% of its surface). It is really a lot. 

You could think that because we have so much water, we probably don’t need to save it. There is more water than land, therefore enough water for people and animals for many years. It would seem so at first glance. But… 


Put on a board the illustrations of a castaway and a waterdrop. Say you are pouring all the water from the Earth into this very drop. Also display the illustrations of water on the carpet or hang them on the whiteboard.

Let’s assume that this drop (Annex 2.1) represents all the water on the Earth. Huge hectoliters of water used by all animals and plants on Earth.

– An overwhelming majority (96%) of the water on our planet is salt water. (Ask selected children to find an illustration of the sea or ocean and place it next to the largest part of the drop that represents salt water). This water is not drinkable as we will see in the moment.

– The remaining small fragment (3%) is fresh water. But… 

– More than half of the fresh water (68%) is accumulated in glaciers in the Arctic, Antarctic, Greenland or high in the mountains. (Ask selected children to find an illustration of a glacier and place it next to the part of drop representing fresh water). The water hidden in the glaciers is very useful. The white surface of the glaciers reflects sunlight and keeps the Earth from being “hot as an oven”. However, we must remember that we cannot drink water from glaciers. – Only the small part, that is left, represents underground water (we reach it by drilling wells), water in lakes and water in rivers, that we can drink or use to water plants etc.

But let us see what would happen if we tried to drink salt water from the sea or ocean. Let’s run an experiment: prepare a salt solution with a proportion corresponding to the salt water in the sea (the average salinity of the water in the oceans is 35 ‰, which means 6 g of salt = 1 teaspoon / 200 ml = 1 glass of water). Let the children taste the salt water. Wait for their reactions. 

At the end of the class, together with children, put a flower into the salt water. Check how it looks after 24 hours. With this simple experiment, children will see that the flower fades, despite being in the water all night.


Explain that salt water is not drinkable either by humans, or by plants and animals. Therefore, it is so important to save our precious fresh water and not pollute it. Let’s remember to turn off the taps, replace the gaskets, take quick showers so as not to waste more water. Also let us collect rainwater. Do not let water be lost through pipes as they can go to the rivers and the sea, where we will not be able to use it for drinking and irrigation. 

Excess intake of salt is unhealthy for human beings. Salt is flushed out of the body in urine and urine is made from water in the body. If a person drunk salt water (for example from the sea), the salt is removed in the urine. Most of the water, he drank, would flush the salt out of his body, leaving little water for vital organs such as the heart, kidneys, and other important organs of the body. Without water, humans die. Our organs need water to function well. The above brings us to a conclusion: if someone becomes lost at sea on a raft, he could die of thirst within a few days, despite having hectoliters of sea water all around. At sea, it is easier to catch fish and satisfy hunger than to quench thirst. 

The post was created as part of the project “I love Warsaw – I’m catching rainwater” financed by the Veolia Foundation.


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