The mysteries of water

Water’s unusual behaviour

Water is one of the few substances on the planet whose chemical formula almost everyone knows: H2O. But this apparently simple liquid, made up of two hydrogen atoms and one oxygen atom, defies the rules of most elements and continues to fascinate those who study its characteristics in depth.

From the outset, it is unusual to find an element that is easily found in liquid, solid and gaseous forms. There are substances that can assume one state or another, but only change shape under the influence of extreme temperatures or conditions.

And there are other chemically unique phenomena relating to water. One of them is the fact that water becomes less dense in its solid state and therefore floats on top of liquid water, which allows the bottom of lakes and oceans not to freeze and to remain full of life all year round. And this also made it possible for complex forms of life to survive over the centuries, despite successive glacial periods. On the other hand, most substances contract when they freeze, but water expands because its molecules take on a crystallised lattice shape with a hexagonal structure.

Its thermal behaviour is also interesting: compared to air, water needs more heat to increase in temperature, taking longer to heat up. That is why the air in contact with the ocean stays cooler during the day than the air over land, with the water serving as a temperature regulator in coastal areas.

What is even stranger, because it seems to go against the laws of thermodynamics, is the fact that hot water, under certain conditions, freezes faster than cold water. This has been called the Mpemba effect, named after the 13-year-old who discovered in a classroom experiment in Tanzania in 1963 that hot ice cream froze faster than cold ice cream.

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The power of attraction

Water breaks all the rules that chemists have been formulating since the 19th century about what liquids can do. It all starts with the light atoms that make up the water molecule – hydrogen and oxygen – and which, under the environmental conditions of the Earth's surface, would make more sense to give rise to a gaseous substance. This is the case, for example, with hydrogen sulphide (H2S), even though it has twice the molecular weight of water, and with other molecules of a similar size, such as ammonia (NH3).

The explanation for this strange behaviour appears to be the substance’s intriguing capacity for attraction. Each water molecule can form up to four bonds between its hydrogen atoms and the oxygen atom of another molecule, which collectively forms a unique cohesion and explains why water is found in a liquid state on the planet's surface.

This strong bond between the molecules is clearly visible in the surface tension of a body of water, which is much higher than that of other liquids and allows insects, for example, to glide across it without sinking. It also makes water difficult to compress and therefore easy to move by applying energy from one side – it is this principle that makes it possible for it to flow out of our taps.

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An essential element for life

As well as accounting for 60 to 75% of the human body's weight and playing an essential role in the structure of cells, almost all the chemical reactions in the processes that give rise to and maintain life take place in water solutions. Together with enzymes, water is able to break down molecules in the body, transforming, for example, carbohydrates into glucose or fats into their constituents glycerol and fatty acids.

Furthermore, water is considered a universal solvent – due to the fact that it not only naturally clings to itself, but also to almost everything it touches – and it has the incredible ability to dissolve various substances, which allows it to transport nutrients and minerals within living organisms. This movement is possible thanks to the aforementioned links between hydrogen atoms, which allow the molecules to pull each other through the body's tiny blood vessels, even against the force of gravity. A phenomenon that also occurs in plants, which are able to draw water from deep in the soil to feed their branches and leaves with nutrients.

It is also thanks to the polarity of the water molecule – with a positively charged region near the hydrogen atoms and a negatively charged region near the oxygen atom – that this liquid is effective as a solvent for ionic compounds (those that contain mineral elements) that are fundamental to health, such as sodium chloride, i.e. common salt.

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The water we need to protect

Water is an essential and scarce commodity. Although it covers 71% of the Earth's surface, only 3% is fresh, of which 22% is in aquifers that are difficult to access and 77% is ice. Less than 1% of the planet's water is directly available for human consumption.

According to the 2023 report by the Intergovernmental Panel on Climate Change (IPCC), approximately half of the world's population suffers from a serious shortage of water for at least part of the year. The World Health Organisation reported that in 2022 there would be 2.2 billion people without safe drinking water.

With climate change, periods of scarcity will be an increasingly frequent reality at global level, and, at the same time, water is increasingly accompanied by pollutants. It is therefore essential to find innovative strategies for managing and also reusing this resource.

Companies such as Bondalti Water – which specialises in solutions for the Integrated Water Cycle – offer cutting-edge technology for the treatment and purification of water, as well as its reuse, guaranteeing a balance between economic growth and caring for the environment.