Sailors and shipbuilders were the first to think about how to desalinate the water of the seas and oceans. Indeed, for sailors, fresh water is the most valuable cargo on board. You can survive during a storm, endure the heavy heat of the tropics, survive separation from the earth, eat corned beef and crackers for months. But what about without water? And hundreds of barrels of ordinary fresh water were loaded into the holds. Paradox! After all, there is an abyss of water overboard. Yes, water, but salty, and to the point where it is 50 to 70 times saltier than drinkable water. It is natural, therefore, that the idea of desalination is as old as the world.
Even the ancient Greek scientist and philosopher Aristotle (384-322 BC) wrote: “Evaporating, salt water forms fresh water ...” The first experience of artificial water desalination recorded in written sources dates back to the 4th century BC.
The legend says that St. Basil, who was shipwrecked and left without water, understood how to save himself and his comrades. He boiled sea water, saturated sea sponges with steam, squeezed them out and got fresh water ... Centuries have passed since then and people have learned how to create desalination plants. The history of water desalination in Russia began in 1881. Then, in a fortress on the shores of the Caspian Sea, near present-day Krasnovodsk, a distiller was built to supply the garrison with fresh water. It produced 30 square meters of fresh water per day. This is very little! And already in 1967, an installation was created there, which provided 1,200 square meters of water per day. Now more than 30 distillers operate in Russia, their total capacity is 300,000 square meters of fresh water per day.
The first large plants for the production of fresh water from sea appeared, of course, in the desert regions of the world. More precisely - in Kuwait, on the shores of the Persian Gulf. Here is one of the largest oil and gas fields in the world. Since the early 1950s, several seawater desalination plants have been built in Kuwait. A powerful distillation plant in combination with a thermal power plant operates on the island of Aruba in the Caribbean. Now desalinated water is already being used in Algeria, Libya, Bermuda and the Bahamas, and in some parts of the United States. There is a seawater desalination plant in Kazakhstan on the Mangyshlak peninsula. Here, in the desert, in 1967, a man-made oasis grew - the city of Shevchenko. Among its main attractions are not only the world-famous powerful nuclear power plant, a large seawater desalination plant, but also a carefully thought-out water supply system. There are three water lines in the city. One is high-quality fresh drinking water, the second is slightly brackish, it can be washed and watered plants, the third is ordinary sea water used for technical needs, including sewerage.
Installation for water desalination at the Shevchenko nuclear power plant (1982).
More than 120 thousand people live in the city, and each of them has no less water than Muscovites or Kievans. Enough water and plants. And to drink them is not such a simple matter: an adult tree drinks 5-10 liters per hour. But nevertheless, for every inhabitant there is 45 square meters of green space. This is almost 1.5 times more than in Moscow, 2 times more than in Vienna famous for its parks, about 5 times more than in New York and London, 8 times more than in Paris.
Water is vital for every person on the planet. Unfortunately, it is not available to everyone. But a new invention developed by a research group at the University of Alexandria in Egypt could change that.
Operating principle
The technology uses a desalination technique called pervaporation. Salt is removed from seawater using specially designed synthetic membranes that filter out coarse salt particles and impurities. The remaining salt is heated, evaporated, and then condenses back into pure water.
In developing countries, investing time and money in the development of water filtration technologies is critical. However, the technology must be accessible and easily reproducible. Fortunately, the membranes involved in this new invention can be made in any laboratory. They can be made from inexpensive materials available locally. More importantly, the evaporation process does not require electricity, which makes this method of drinking water treatment cheap and suitable for areas where there is no electricity supply.
In addition, the researchers discovered another interesting feature of this technique. It is able not only to filter out salts, but to remove other pollutants.
Efficiency
According to Helmi El-Zanfali, a professor at the National Research Center in Egypt, the technology implemented in the study is much better than the reverse osmosis technologies currently used in both Egypt and the Middle East and North Africa. Using this development, it is possible to effectively desalinate water containing high concentrations of salt in the Red Sea, where desalination is more expensive.
At the moment, the technology is not yet ready for domestic use. The development has been proven in theory to be effective, but large-scale demonstrations and action plans have yet to be made to deal with the waste.
Getting drinking water on a desert island is not easy, but it is quite feasible
If you were on desert island, then with some wit and a container made from leaves or sunken fruits, you have a good chance get fresh water and stay alive for many days. To turn salt water into drinking or fresh water, you need to rely on the principles of nature. During the evaporation of sea water, pure water is collected, and salt remains. The following process is based on the solar desalination method to collect water for drinking in an emergency.
Instructions on how to get drinking water
1. Dig a hole to collect water. The hole should be at least 1 meter deep and wide enough for you to reach the bottom with your hand. As soon as you get close to 1 meter, you should see very wet sand or a puddle of water. Take your time, as you are limited in water, and the tension will cause thirst ahead of time.
2.Place the container in the center of the hole. The container can be a hollowed out coconut, fruits or large leaves. If there is enough vegetation on the island, then you can add it to the hole around the tank. The water from the vegetation will evaporate and accumulate in the vessel.
3. Cover the hole and bend the cover. Place a large leaf (for example, from a palm tree) on the hole and cover it as completely as possible. Secure the outer edges of the sheet with stones. Place a few pebbles in the center of the lid to create a small indentation above the bowl. This will direct the water into the vessel. During the day and night, dew and condensation will collect on the makeshift cover and drain into the vessel.
4.Periodically remove the container from the pit to drink water or fill other containers for later use. Place the vessel back into the hole to continue accumulating water. The water will be safe to drink. No
Water- the source of life for all living things, but you need to distinguish which water is useful and which is not. Approximately 99% of all the waters of the earth is the water of the oceans and seas, that is, salt water, is unsuitable for consumption. Many people in the world need living, fresh water, and today we will tell you how to get fresh water from salt water.
How to make fresh sea water at home?
Fresh water differs from salt water in the amount of salt and other chemical elements. The most popular way is to separate salts from water by distillation.
This method consists in heating water to the boiling point, and collecting vapors in the form of condensate. This method is well described in the article -
.
There is also another way, the so-called - desalination. It consists in the fact that salt water is passed through a membrane that can only pass pure water without salt components. But this type of purification is not very effective, since the membrane passes a very small amount of water over a long period of time.
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We live in a unique place - the Earth, which, although it has a lot of land, is still mostly covered with water. We swim in it, we navigate it, and most importantly, we drink it. Unlike many animals, we are unable to get enough fluid just from fruits and vegetables – we need to drink regularly to stay hydrated. But only the body of water has another unique property - it is almost all salty. The percentage of fresh water is surprisingly small. Yes, we are used to it, because such water enters our homes and is sold in stores. But what if we suddenly did not have access to fresh water, if we only have sea water? Then it needs to be refreshed. Let's see how this can be achieved.
You will need:
This method is also called sublimation. It is easy to implement even at home, although it will not provide a large amount of liquid.
Take an ordinary saucepan, into which salt water is poured. Next, you need to cover this pan with a lid and put on fire. Gradually, condensation will accumulate on its cover.
However, even when the lid is removed, most of the fresh drops will flow back into the pan, so this impromptu device needs to be slightly improved.
- A hole is drilled in the lid of the pot.
- A flexible tube is inserted into it, for example, a coil from a moonshine still.
- Its other end is lowered into an empty vessel.
- Next, you need to cover the tube with a damp cloth so that the steam in it cools.
- It will condense and fall into an empty vessel.
As a result, only salt will end up in the heated pan, and only distilled water will remain in the second vessel.
Please note, however, that there will be no salt in such a liquid at all, and therefore thirst will be quenched poorly.
It is better to pour a small amount of salt water into it. 
With this method, special precipitating reagents are used. They interact with the salts found in sea water and form compounds that are insoluble. Therefore, they settle and they can be filtered out without any problems.
This approach has its disadvantages, in particular, the high cost of reagents, the slowness of the reaction, a large number of necessary reagents.
Therefore, this method is used very rarely, but in everyday life it is not used and almost never at all.
This method is predominantly industrial and has been used for a long time. It is based on the use of two semi-permeable membranes made of cellulose acetate or polyamide. Small water molecules can pass through them without any restrictions, while larger salt ions, as well as other impurities, are trapped and prevented further. 
It is difficult to achieve desalination of a large amount of liquid in this way, and in everyday life such a method is difficult to implement - it is suitable for industrial enterprises.
This desalination method seems to be very simple in its idea, but in its implementation it is quite labor- and resource-intensive. The idea is based on the fact that salt does not get into the ice when frozen, because the formation of ice occurs only from water molecules.
The largest amount of fresh water in nature is found in all kinds of glaciers.
Usually the Eskimos resort to this method. They expose a container of salt water to frost, and then wait until ice crystals form there. This ice is collected and melted - and the water is drinkable. 
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