The science of water

At a time when the country is talking about monsoon and rains, it is worth examining water - one of the strangest molecules we know. At one level it is simply two hydrogen atoms bound with one oxygen atom, attached to each other to form a molecule that has the shape of an isosceles triangle. At temperatures we encounter on earth, it is largely found in liquid form, but is also found in the form of snow and some amount of it is also found in the air as moisture. It is the only substance on earth that is found in all four forms of gas, liquid, powder and solid in any significant quantity.

But water is strange in many ways that are crucial to life on Earth. Take its overall behaviour. If you normally take any material that is in gaseous form, the molecules of the material will collide with each other at a certain speed which ensures that they bounce off each other and remain free. As you cool the gas, the molecules lose their momentum and when they collide with each other, they stick to each other making a heavier unit that then settles down under its own weight in gravity and we get a liquid. When we cool the liquid, the molecules tend to bundle up and move so slowly with each other that they become locked with each other and become solid. This is a natural and understandable sequence and is the most common behaviour of matter. However, in this sequence we also assume that as the atoms come close to each other, they are packed increasingly strongly and the density (number of atoms in any volume) will increase with decreasing temperature, with two marked phases when it goes from gas to liquid and from liquid to solid.

In water, something strange happens. The gas to liquid phase is more or less as expected, but when you cool liquid water below 4 degrees centigrade, things change. The water molecules will now tend to separate out from each other as we cool further and make ice. This is the triple point of water where within the same complex, one can find molecules stuck to each other loosely as in liquid, as well as some free floating molecules of water as in water vapour and some molecules rigidly bound to each other like in solid ice, not to mention small icicles. There are very few substances that can do this. When you cool it below this, the water in fact becomes less dense, to the extent that the density of ice is less than the density of water and hence ice floats on water. Some metals which melt at high temperature and cool rapidly do have such an effect and they, for example, make Moon a little fluffier. This curious fact is crucial to life on earth. If lakes and other water bodies were to freeze bottom up instead of forming a layer of ice on top, life would have long since frozen to death in cold regions.

When water is cooled in an environment where the density of water vapour in the atmosphere is low, we get a very fluffy form of water that we call snow. On the other hand, if you take a large quantity of water and then freeze it, we get ice. Snow is light and fluffy and has low density and hardness. It is also firm to walk on. Compared to this, ice is hard and transparent or at least translucent. One can scrape ice and make it feel like snow and compress snow to make it into ice, but the beauty of snow particles is unique and water molecules can combine in so many ways that it is said that no two snowflakes are the same. 

Another feature of water is the unusually high specific heat of water. Water can absorb enormous quantities of heat and not become hot. This too is important for life on earth. If water also got hot as quickly as, say a piece of metal, the landmass of earth would have remained lifeless. Because water can absorb a lot of heat compared to land, the same amount of sunlight falling on both will heat up the landmass very quickly and hence the air above it will be hot compared to the neighbouring sea or pond. As a result, the cold air above the water body will move over the hot land and carry with it a lot of moisture that will provide water to the soil. 

Water is also unique in that it is a universal solvent. Almost anything can be dissolved in it. This again, is crucial to life since we believe that life originated in the seas and to make all the complex molecules of life, it was necessary that they are easily available. Water, which is neither acidic nor basic and yet an excellent solvent, provides this perfect environment for life to arise.

In space stations, which are essentially in free fall around the earth – like a projectile that goes just above the horizon – it experiences practically no gravitational pull. So water behaves strangely there. Even a casual search for water in space on any internet search engine will lead you to several excellent films on NASA Space Station experiments with water. In the absence of gravity, water can form nice spheres of water which can then float around and does not interact easily with other things. In fact, water molecules tend to be so tightly bound to each other and to the surrounding medium that they tend to climb up in thin capillary tubes. So while normally water finds its own level, in capillary tubes they will have uneven heights. 

All this strangeness makes water an excellent medium for life to evolve. While life itself is made of carbon, since only carbon can make the long chained molecules crucial to life’s processes, water provides an ideal base on which the scaffoldings of life can be constructed. Even the land-living humans are made up of 80% water. That is why there was so much excitement when Chandrayaan pinpointed water on the Moon. 

However, it is an interesting fact that when planet Earth was formed some 4,500 million years ago, it had no water – the Sun shining down on the small, still evolving Earth would have chased away all water, far into the deep space. The water that we see on Earth today, was largely delivered by a couple of comets and some through chemical reactions on the cooling Earth. If these carriers of water had not arrived with just the right amount of water, Earth would either have been completely covered with water or the little bit of water would have also sizzled away, like water on a hot plate. But water as a molecule is very rugged, we have seen it almost everywhere in the Universe, from the dark spots on the Sun to some of the farthest quasars some 2 billion light years from us. 

In all religions, water is considered as purifying, where any sin or any act that makes something impure, can be purified by washing it with water. Yet, pure water is the ultimate poison as your body cells will not be able to prevent it from entering the body cells and bloating them to the point of explosion. Fortunately, water is such a good solvent that it is impossible to get it in a pure form. Even if you make pure water, it will quickly absorb surrounding gases and by the time you are ready to drink it, it will be ready to quench your thirst without harming you.

Water is crucial to life on Earth. All life on Earth needs water for its smooth functioning. Most of us cannot even handle very salty water as it would make us thirstier. But the irresponsible use of water by humans has caused a stage where we are staring at the possibility of water wars. Aggressive arguments between various states of India are well documented, but problems between nations are also beginning to get more severe. This should make us sit up and begin to care about our precious resource.

Water is truly a wonderful medium. This colourless liquid that is tasteless to our tongue (the taste comes from the dissolved material) is crucial to life. It has been referred to in some strange ways in our literature. For example, when asked “pani re pani tera rang kaisa?” (water, or water, what is thy colour?) in the film Shor, Indrajeet Sing Tulsi responds – “Sau saal jine ki ummidon jaisa” and adds in good measure “jab tu phire umeedon par, tera rang samajh na aaye (when you run over hope, we cannot fathom your nature)”.

Truly, if there was a god who designed the universe, water would be his or her greatest creation.