How does groundwater become salty?
Colorless, pure and cool, without odor and without taste - this is how drinking water should be. It must not contain any pathogens, but certain minerals such as calcium, magnesium and fluoride. To ensure that the quality of the drinking water is right, it is constantly examined in the waterworks laboratory. In Germany, drinking water is the best controlled food.
Drinking water does not bubble out of the tap by itself. It must first be processed so that it meets the high quality requirements. Groundwater is best suited for the production of drinking water. Because the rainwater seeps into the ground, as if through a filter, is pre-cleaned. Pollutants and turbidity that are still in the water afterwards get caught in the filters of the waterworks. The clean water can then be sent on its way to the individual households via pumping systems.
Drinking water can also be obtained from rivers and lakes or from the sea. However, the water from these bodies of water is usually not as clean as the groundwater. In addition, seawater has to be desalinated before it can be drunk.
Singapore is not poor in water. On the contrary: it is surrounded by the sea. But what the city of 5 million does not need salty sea water. Drinkable fresh water is in demand. That is why the city-state built a huge dam for its water supplies: "Marina Barrage"!
So far, Singapore has bought almost all of its drinking water from neighboring Malaysia. From there, millions of liters flowed into the city every day. But Singapore wants to make itself independent from Malaysia, because the relationship is tense. For this reason, the city began building a gigantic dam wall in 2005. A 350 meter long reinforced concrete dam now shields the Singapore River from the open sea. Nine movable gates control the water level. Huge pumps can transport the water masses into the sea in the event of a storm surge or tropical precipitation. Behind the huge “Marina Barrage” wall, a freshwater lake has arisen in the middle of the city. Even if the water is still brackish and salty at the moment: From 2015 the “Marina Reservoir” reservoir will provide clean drinking water.
Marina Reservoir and the accessible Marina Barrage dam have become a tourist attraction. The residents of Singapore also use the site in their free time. But only electrically powered boats are allowed to travel on the lake. After all, in the future it should help to quench the tremendous thirst of an entire city.
No land in sight
Nowhere in the world are you further from the mainland than at Point Nemo. That is why it is also called the pole of water or the pole of inaccessibility. Point Nemo is located in the middle of the Pacific Ocean between Chile and New Zealand. It is exactly 2,688.22 kilometers away from Easter Island, Ducie Island and Maher Island. If you want to visit Point Nemo, you should remember its coordinates: 48 ° 52.6 'South and 123 ° 23.6' West. However, if you approach it, you will find nothing but water!
What water can do
No matter whether we drink tap water, jump into a lake or are surprised by a downpour - we are constantly in contact with water. And not only that: we are made of water ourselves, around two-thirds of it. Without question, water is part of our everyday life. But what seems completely normal to us has all kinds of peculiarities. And the water owes this primarily to its structure.
Everything that exists on this earth is made up of tiny building blocks, the atoms. This is also the case with pure water: It is a combination of two hydrogen atoms and one oxygen atom. These combine to form a water molecule, H for short2O. The individual water molecules are only loosely connected to one another.
This loose cohesion ensures that the connection between the molecules breaks at high temperatures: the water evaporates. If, on the other hand, it cools down significantly, the molecules organize themselves into a solid, regular lattice, the ice. The special thing about it: In its solid form, water has a larger volume than in its liquid state.
The arrangement of the water molecules also ensures another property: the surface tension of the water. Because of this tension, water spiders and water striders can easily walk on a pond. But water can do even more: it is able to dissolve substances. Small grains of salt or sugar dissolve completely in water. Sea water, for example, contains large amounts of salt that we can taste but not see.
We owe the fact that lemons ripen on the island of Mainau on Lake Constance to another ability of water: it can store heat. Lakes or seas heat up in summer and keep the heat for a long time. That is why the temperatures on the coast fluctuate less than inland. Far from the coast, the temperature differences between day and night and between summer and winter are much greater than near the sea.
How does the salt get into the sea?
Anyone who has swallowed water while bathing in the sea knows from their own experience: Sea water tastes salty. And when the water evaporates, a fine white layer of salt often sticks to the skin. This is because, on average, seawater consists of 3.5 percent salt. For one liter of sea water that is 35 grams or about one and a half heaped tablespoons of salt. But how does the salt actually get into the sea?
Many of these salts come from the rocks of the earth's crust. Rainwater dissolves salts from the rock and takes them with it. It washes them into rivers and into the groundwater. This is how salts are washed into the sea. Because relatively little salt is transported, the river water is hardly salty. Only in the sea does the concentration increase. Because there are also salts from the ocean floor and submarine volcanoes. When the sea water evaporates, all of these salts are left behind. That is why washed-out salts have been accumulating in the oceans for millions of years.
The salinity is not the same in all seas. The more water evaporates, the more salty the water becomes. The Red Sea contains more salt than the Pacific. And the Dead Sea in the Middle East - actually a lake - is so salty with a salt content of around 30 percent that you can lie in it without sinking. The Baltic Sea, on the other hand, is rather poor in salt: because of the low temperature, very little water evaporates there. In addition, many rivers flow into the inland sea and feed it with fresh water. That is why the Baltic Sea is much less salty than the Dead Sea.
How sweet is fresh water?
It doesn't taste sweet at all, but it's called fresh water. In contrast to salt water, it contains no or only very small amounts of salt and therefore has hardly any taste. For this reason it is also well suited for the production of drinking water.
Fresh water is rare: only two to three percent of all water on earth is fresh water. Most of it is in the high mountains and at both poles. There it is stored as ice in glaciers. Only a very small fraction of the fresh water on earth flows in streams and rivers or splashes in lakes and groundwater. The water in clouds and precipitation is also "sweet".
Fresh water is vital to us. To stay healthy, a person needs about two liters of fluid per day; without water it can only survive five to seven days. In addition, we need a large amount of fresh water for showering, washing clothes or washing dishes. Plants and animals that we feed on also live from water. Freshwater is even a habitat for many living things: crayfish, pond and river mussels and freshwater fish such as trout, pikeperch and char.
How is groundwater created?
Like water in a sponge, groundwater collects in small and large cavities under the earth. It occurs when rain or meltwater seeps into the ground or when water from streams, rivers or lakes flows through crevices into the subsoil.
Depending on whether the soil consists of loose sand or dense soil, the water descends faster or slower. And only when the downward flowing water hits a water-impermeable layer of rock such as clay, the seepage is stopped. Then the groundwater collects in the cavities of the ground above the impermeable layer and is stored therein. If the layer of “watertight” rock slopes down, the groundwater flows even down the slope towards nearby streams and rivers. The places where the groundwater emerges from the surface are called springs.
When it rains very heavily or a large amount of snow melts, more water collects on the earth's surface in a short time than can seep away. Then the water backs up. If it cannot drain away quickly enough, it will cause a flood.
As the groundwater flows through the various layers of the earth, it is filtered and purified. This is why drinking water can be obtained particularly well from groundwater.
The groundwater is part of the water cycle. It can stay inside the earth for less than a year or several million years. Under the Sahara, for example, researchers have discovered groundwater that has been under the desert sand for many thousands of years.
The unequal distribution of drinking water
Turn on the tap and fill up with clean drinking water: it's not as easy everywhere on earth as it is here. Because although most of our planet is covered by water, there is a lack of water in many regions of the world. Today, over a billion people already have no access to clean drinking water.
So far, the water shortage has been particularly severe in the dry areas of Africa, where it hardly rains. Here people often have to walk for kilometers to the nearest river or well. But there is also a lack of water where fresh water is contaminated by bacteria. The affected countries often lack the money to purify the water in sewage treatment plants, as we do in our country, or to desalinate seawater.
Water consumption is very different in the individual regions of the world. The industrialized nations consume much more water than the developing nations. When it comes to water consumption, it is not just the water used for drinking and washing that is important. Wherever a lot is consumed, “virtual water consumption” is also highest. Because much more water is used to manufacture the products than you can see at first glance. This invisible water that is used in production is also called “virtual water”.
Experts suspect that more and more people will suffer from water shortages in the future. The growing world population and the pollution of the water are decisive reasons for the increasingly scarce supplies. But global warming is also likely to worsen the uneven distribution of water. In regions that are already flooded regularly, rainfall will increase. And very dry areas are likely to get even less rain.
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