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A large part of Earth's surface is covered by water. So why do some countries experience water shortages?


Look! Now it's NORMAL again! What! This morning when I took it out of the freezer, the bottle had grown. It looked like it would - POFF!

burst. So... maybe some water leaked out? Naah. The ice seems to take up less space when it's melting.

Right! Let's zoom in on that bottle! Because - when water freezes to ice, the water molecules form a regular pattern -- a crystal. And when the water molecules are structured in this crystal pattern, there is some empty space between them. But when the ice melts, the water molecules become jumbled and get closer to each other again, - taking up less space.

Okay, but most importantly - the water is COLD! That's a second important property of water. It takes a lot of energy to heat up water -- or to make ice melt. That's why the water in the bottle was cold long after Leon took it out from the freezer. Sooo...

it floooats! Explain THAT! Okay! Water takes up more space when in solid form than as a liquid, remember? So ice is lighter than water -- it has lower density.

Water is peculiar in that sense. Most substances have higher density when in solid form than as a liquid. Ice is so light that it floats on top, and insulates the rest of the water from the cold air. This is what allows fish to survive the winter - even if it's really cold and the water freezes over. Water is also the only substance on earth that occurs naturally in all of the three common states of matter: Solid, as ice, Liquid, as water, And in gaseous form, as steam.

A thermometer, if it's measuring temperature in Celsius degrees, is based on water's states of matter. When water freezes the temperature is zero degrees Celsius. And when water is boiling the temperature is one hundred degrees Celsius. But if I heat the water very, very much, then the water gets even warmer, right? Most often not.

When water is boiling, it transforms to gas. So boiling water normally won't get any hotter than one hundred degrees. Yet at the peak of a tall mountain, water boils at a lower temperature. Up there, the pressure of the air against the water is much less. And conversely, if water is enclosed and under high pressure, then it can reach temperatures higher than 100 degrees Celsius, without transforming into gas.

Lucky us that there's so much water. I mean, we use it for everything: drinking, washing, watering plants. And we can eat the fish in the lake! The most important use of water is actually as means of transport. Not just for boats.

In plants, humans, and animals, water helps by transporting all kinds of important substances. Without water -- no life. As much as 70 per cent of the surface of the Earth is covered by water. Mostly oceans -- but also lakes and rivers. Still there's a shortage of water in many areas.

Firstly, almost all the water is in the large oceans -- and they are salty. You can't drink salt water, nor water plants with it. A mere three per cent of the earth's water is drinkable, fresh water. But it's trickier than that! Most of the fresh water we can't even get to!

It's in the form of ice, at the poles. Or so deep down into the ground, that we can't ever reach it. That's why there is a shortage of water in many populated areas, or where there's a lot of farming. And in many places, rain comes rarely. There, you have to drill deep into the ground to get water.

Mmmm. But now we've forgotten another important PROPERTY of water! - Uh huh? - Last one in's a rotten egg!