About the Author

Dr Julian Caldecott is an ecologist with a mission to help reduce and repair the damage that we are doing to the biosphere – the thin skin of life on Earth. He’s spent years doing this through projects in tropical countries where the pace of environmental destruction is often fastest. His recent work as a senior consultant to the UN Environment Programme has aimed to restore natural ecosystems so as to reduce disaster risks and increase environmental security in the face of climate change. Julian sees the global water crisis as an outcome of humanity’s unbalanced relationship with the biosphere. To correct this, he believes that the most important need is for public understanding of the values, functions and fragilities of nature, upon which effective action can be built. His books, which include Deep Water, Designing Conservation Projects and the World Atlas of Great Apes, aim to promote both understanding and action. Visit his web-site for more details:


Photograph © Alice Mutasa (

About the Book

All known forms of life depend on water

Water is a basic necessity of life, yet 1.2 billion people currently live without a safe water supply, the amount of available drinking water is shrinking and the need for it is increasing relentlessly. Our oceans have become a global fish quarry and a rubbish dump, and while some countries are flooding with over-abundant rain, others continue to suffer drought and famine. We are experiencing a global water emergency.

Exploring the history, science, economics and politics behind the looming water crisis, and the tragedies – both small and large – that are its result, Julian Caldecott reveals where the water we use comes from, and at what cost. His ardent call-to-arms reveals how we can all make a different to the way water is used and abused on our planet.

‘This fascinating book explains not only why we need to restore balance, but more importantly how we can do it.’

– Zac Goldsmith, Director, Ecologist

Praise for Water

‘A brilliant overview of an enormous subject.’

– Steven Poole, Guardian

‘Should be read far, wide and as soon as possible . . . it does an excellent job of promoting a rational, effective, trans-ideological approach to environmental decision making.’

– Miguel Mendonça, Resurgence

‘Caldecott keeps a masterly hand on the reins of what is a vast topic . . . With laudable dexterity, [he] moves from the very small to the very large, from the interactions of atomic particles to the role water plays in the biosphere.’


‘A prophetic read.’

– Edward P Echlin, ecological theologian and author of The Cosmic Circle

‘Includes a lucid presentation of the Aquatic Ape Theory . . . The book shows that we can avoid disaster if we come to our senses and give Gaia a helping hand.’

– Elaine Morgan, evolutionary anthropologist and author of The Descent of Woman and The Scars of Evolution


Life in Every Drop

Julian Caldecott

First published in Great Britain in 2007 by Virgin Books
an imprint of the Penguin Random House Company

This edition published by Virgin Books 2008

For Moyra

‘The whole world has now become like one
family, almost like one body. So some
destruction of some other part of the world is
actually destruction of yourself.’

His Holiness Tenzin Gyatso,
the 14th Dalai Lama of Tibet


‘The way we use water is a measure of us.

Satish Kumar, Earth Pilgrim



About the Book

About the Author


Title Page


Measuring Water and Land


1. What is Water?

2. Water in the Biosphere

3. The Experience of Water

4. Ocean Water

5. Swamp Water

6. Lake Water

7. River Water

8. Ground Water

9. The World to the Rescue?

10. People to the Rescue!

Appendix 1: Glossary

Appendix 2: Reading List




Measuring Water and Land

1 cubic kilometre (km3)=1 billion cubic metres (m3)=1 billion tonnes of water

1 m3 of water=1,000 kilos=1 tonne of water

1 gigalitre=1 billion litres=1 million m3=1 million tonnes of water

1 square kilometre (km2)=100 hectares (ha)=247 acres=0.386 square miles

1 ha=10,000 square metres (m2)=2.47 acres=0.004 square miles


For explanations of key words used throughout this book, see the glossary in Appendix 1.


As I write this, Britain is having a crash course in water awareness. Many of this book’s themes are suddenly becoming all too familiar. We have realised, for example, that our vulnerability to flooding is made worse by building on floodplains, by channelling rivers through narrow, artificial banks, and by covering ground with tarmac and concrete, thus preventing it from absorbing water. We’ve learned the irreplaceable value of clean drinking water, and we are coming to realise that climate change is steadily demolishing our expectations about a gentle English climate.

Water is an extraordinary substance that makes life on Earth possible. But almost all the world’s water is salty, and for us on land a regular supply of fresh, clean water is uniquely precious. Such a supply is the most important service that an ecosystem can offer, yet is often allowed to lapse through abuse, or it is diverted from those who really need it, or destroyed by over-use or pollution. As a result, over a billion people now have no access to clean water and 2.6 billion have no effective sanitation system. One consequence is a huge waste of human energy in an endless quest for water, a burden that often falls hardest on women and children. Another is unnecessary illness, which every year claims the lives of nearly two million children. We are, in every sense, facing a global water crisis.

Yet, as Julian Caldecott explains here, this global crisis is in fact made up of tens of thousands of local water crises, each one due to decisions that affect local ecosystems. Water and ecosystems are linked, from the boundaries of each catchment to the streams, rivers, lakes, floodplains, swamps and estuaries created by water. Everything we do in a catchment affects what happens downstream, so logging, farming and grazing, applying fertilisers or pesticides, dumping garbage, releasing sewage or spilling chemical wastes all have an impact that’s conveyed by the ultimate solvent, water. Meanwhile, we’ve taken to pumping water from the ground at rates far higher than it’s being replaced, causing wells to run dry in region after region.

This book is about human decisions. Julian Caldecott draws stories from all over the world, and reveals the many ways in which our experience of water is a common one. He shows how different approaches can have different outcomes, some destroying ecosystems, some transforming them, some sustaining them. But there’s also a bigger context. The viability of the biosphere depends fundamentally on water – often in ways that we barely understand. Water, ecosystems and climate are inextricably linked, so we need to make wise decisions about all three. Local ecosystems determine whether or not there’s water in your well, river or tap, and help dictate rain or drought, storm or famine. All the evidence is that the negative changes we make to our environment are contributing to mass extinction, local water crises, and further climate chaos.

This fascinating book explains not only why we need to restore balance, but more importantly how we can do it.


Zac Goldsmith

Director, The Ecologist

London, July 2007



What is Water?

WE THINK WE know water. We take it in through almost everything we drink or eat. We wash in it, swim in it, float on it. We wish it would stop falling on our heads, or hope it will start. We know that we have to drink several litres of it each day, depending on heat and sweat, for if we don’t we are first driven and then tormented by thirst. We know that there’s water in everything that comes out of our bodies, from blood and breath to tears and spit. We know that we must water our plants if the rain will not, and that we must bring our pets and livestock to water every day. We know that things that are plump and moist are usually alive, and that things that are shrivelled and dry are usually dead, or waiting for water to make them good again. We know that rivers flow downhill, and that there are fish in them, and otters or platypuses near them. We know that the ocean is vast and powerful, and that there are whales and sharks in it. We know that water is potent and symbolic, for we dab it on our heads or sprinkle it on the ground during rituals.

We know a lot about water without really thinking about it. We have an intuitive appreciation of its key role in physiology (because of thirst and sweat), ecology (because of fish and farming), magic (because of rituals and dreams), economics (because we often have to buy it) and power (because we are vulnerable to those who control it). But this everyday experience is just a fraction of the total reality of water and our relationship with it, our collective struggle to understand and use it in all its dimensions. This book explores some of these aspects of water, as seen through the prism of ecology. I chose that particular prism because life, water and ecosystems go together, always. We are alive, and in using water and ecosystems we determine what all life will be like in the future, including our own.

In Chapter 2, we’ll find out about the role of water in the biosphere, the 30 km-deep living skin of the Earth. Here we’ll look at the origin and evolution of life in symbiosis with water, the accumulation of biodiversity over evolutionary time, the devastating culls of mass extinctions, the threat of global warming, and the role of the Earth itself in correcting it if we don’t. Chapter 3 will describe our experience of water in evolution, and its significance for how we think about and try to solve environmental challenges, including the water crises. Other chapters will focus on the main water-bearing ecosystems of our planet: the oceans, wetlands and swamp forests, the lakes and rivers, the ground waters and aquifers, and the farms that they sustain. In each case we’ll look at the natural history of the ecosystems themselves, as well as how people have used and abused the living things and waters within them.

Each chapter will show how a particular kind of thinking leads people to impose short-term demands on nature, with disastrous consequences, and how another, more ecological kind of thinking leads us to more sustainable outcomes. It is the dominance of short-term thinking that has led us to environmental crisis, the solutions to which may be found in re-discovering the other kind of thinking. The last two chapters explore this possibility. Chapter 9 will examine the international efforts we’ve made so far to conserve nature and water, while in Chapter 10 we’ll look at what we can do as societies and individuals to restore the biosphere to harmony, how we’ve solved similar major problems in the past, and we’ll see a vision of what the biosphere might look like in the year 2085 if all goes to plan. The water crisis is deeply challenging, but we can approach it knowing that it, like many of the world’s problems, involves local ecosystems and local communities, so although they are all connected, we do have the power and the precedent to solve these problems bit by bit.

But we’ll start here with where water came from. We’ll then look at its physical and chemical nature and behaviour, to give a raw insight into the properties that make water so important and also so strange. And as we go, we’ll see how each of the extraordinary properties of water contributes to a symbiotic relationship with life itself, from the innermost workings of every living cell, to the physiology of whole organisms and the patterns that sustain ecosystems and, ultimately, the biosphere itself.


Water’s been here on Earth for a long time, and its peculiar properties have always been important to the planet’s evolution. But where did the stuff come from, and how did it get here in such vast and fortunate quantities? In the big picture, water ought to be common, since its molecules are made of atoms of two of the commonest elements of ordinary matter in the Universe: hydrogen, which at 75 per cent of everything is the most abundant element, and oxygen, which at far below 1 per cent is still the third most common (after helium, at 23 per cent).

Hydrogen condensed out of the primal chaos of the Big Bang, a few seconds after the beginning of the Universe. But oxygen and all the other elements with larger and heavier atoms were created much later, in complex thermonuclear reactions deep within stars. When these stars eventually died, the larger ones exploding as supernovas like SN 2006gy, the brightest ever seen, all the elements within them were scattered deep into space. There they accumulated through the slow action of gravity into new generations of stars, as well as into the spinning clouds that would one day become planets and all the other solid forms out there, such as asteroids and comets.

Some of these clouds happened to contain more water than others, and some, after collapsing to become solid, happened to have the right conditions to keep it. The strong gravity field of a massive planet would hold it down, and if there were little enough radiation from nearby stars the water wouldn’t be broken back into separate hydrogen and oxygen atoms. If there was sufficient radiation, the lighter hydrogen atoms would mostly drift off into space, leaving oxygen to combine with something else, and so water would have gradually vanished. A low enough temperature would keep water on the solid planet too, as deep-frozen water mixed with rock is immobile until it gets heated up.

Water has so far been found on three planets: Earth and Mars in our own solar system, and on HD 209458b, a Jupiter-like gas giant located 150 light-years away in the constellation Pegasus (we know this because of the way light is absorbed in the wavelength characteristic of water vapour as it passes across its star’s face). The presence of hot, solid water under great pressure has also been deduced from the density of a fourth planet, GJ 436b, which orbits a cool, red star some 30 light-years away. Water has also been discovered or confidently inferred on or inside several moons, including our own, Jupiter’s Europa, Ganymede and Callisto, and Saturn’s Enceladus and Titan, as well as in several comets.

Moreover, from its light-spectrum signature, water vapour has been detected in the hot atmosphere of our own Sun, and in clouds of inter-stellar gas, both within our own galaxy (such as in the Orion Molecular Cloud, 1,500 light-years away), and in other distant ones (such as the spiral starburst galaxy NGC 253, the elliptical galaxy NGC 1052, and the Circinus galaxy ESO 97-G13). This is a tiny sample of the Universe, but already the hint is there that water is very widespread, and we can expect to find it quite often as our search technologies improve.


In 2005, the US spacecraft Deep Impact launched a 370-kg payload into a head-on collision course with the rocky nucleus of the small comet Tempel 1, and retired to a safe distance. The combined speed of the two objects was about 37,000 km/hour, so a considerable explosion was anticipated. What was not expected was that about a quarter of a million tonnes of water would be blasted from the nucleus, which was not believed to be very icy, and continue to leak out over thirteen days.

It is thought that a more typical comet nucleus fits the description of a ‘dirty snowball’, with Halley’s Comet, for example, having a mass of about 100 billion tonnes, most of it ice, and others being up to ten times as big. A million comets of this size hitting the Earth would have gone a long way to filling the seas. Since comets were common in the inner solar system early in Earth’s history, it’s possible that the planet was hit by a large comet once every thousand years for its first billion years, which would have done the trick.

Not all comets, however, contain water that has the same isotopic composition as water found on Earth, i.e. the same ratio between ordinary water and ‘heavy’ water. The latter is water in which the hydrogen atoms are replaced by deuterium (a stable isotope of hydrogen with an extra neutron in its atomic nucleus). One that did, though, was Comet Linear, which broke apart near the Sun in 2000, yielding a cloud of hydrogen formed by the disassociation of an estimated 3.3 million tonnes of Earth-type water.

It seems likely, therefore, that at least some of Earth’s water arrived when the planet was bombarded by comets early in its history. But there is also evidence for an additional mechanism, in which the Earth’s atmosphere, even today, is being bombarded by small comets made of pure water. Ultraviolet satellite images of Earth’s atmosphere show what look like very-high-altitude holes or vapour trails, hundreds of them appearing each day. These images have been studied since the mid-1980s by a team led by Louis Frank, Professor of Physics at the University of Iowa and a leading authority on energetic charged particles, plasmas and auroral imaging around the Earth and elsewhere in the solar system. Frank and his co-workers interpreted the images as showing the breaking up of small comets. These they visualised as loosely packed ‘snowballs’, 20–40 tonnes in weight, that disintegrate from rapid electrostatic erosion as they approach the Earth and are then vaporised in the upper atmosphere.

Objects of this size are nearly invisible in space, especially if they are coated with dark dust, so direct observations of these comets are unlikely. Further satellite evidence for them was obtained in the late 1990s, however, including signs of water being released at between 960 and 24,000 km in altitude, and a photograph of what could have been the trail of a small comet vaporising over the Atlantic Ocean at between 8,000 and 24,000 km in height. If the interpretations are correct, which is strongly debated, then we’re looking at the arrival of a small water body weighing about 30 tonnes every few seconds – a rate that if sustained could deliver a metre or two of depth to the world’s oceans in a million years.

So all in all we’ve a lot to thank the Universe for, and much to wonder about. We’re made of elements forged within stars and blasted across space by supernovas. One of those elements teamed up with the commonest substance in the Universe to make a compound that is, as we’ll see, both unique and perfect for sustaining life. And wandering comets brought (or maybe are still bringing) enough of it here for the Earth’s particular gravity and distance from the sun to allow the creation of a blue planet.


Water is a truly remarkable substance, with properties like no other. These properties, and the transformations of water from icy solid to liquid, from its liquid state to vapour, and back again, are central to life on our planet. Water’s unique attributes result from the forces at work within and between its molecules, and understanding them is a vital key to making sense of nature. So it’s important to grasp some basics of chemistry – the shape of water molecules, and how they behave in partnership with each other and with other substances – in order to understand why it’s so important for life on Earth.

All chemical matter, including water, consists of elements, either as pure masses of one type of atom, or else, more often, as masses of molecules, which are made of joined atoms. If more than one kind of atom is in a molecule, it’s called a compound. In a molecule, the atoms are strongly bonded to one another, by arrangements based on the rules that opposite charges attract while similar charges repel one another. Since protons in an atom’s nucleus are positively charged, and the atom’s electrons orbiting the nucleus are negatively charged, there is scope for sharing or transferring electrons between atoms that approach each other. In a covalent bond, a pair (usually) of electrons is attracted into the space between the two atomic nuclei. Once there, the electrons and nuclei are pulled together. But the two positively charged nuclei also repel each other, so the two atoms stay at a distance where the attractive force balances the repulsive force: a point of equilibrium.

Although the number of electrons and protons in an atom are usually the same, so the atom as a whole is uncharged, this is not always so. An atom with a charge (either positive or negative) is called an ion, and these are at the root of the other main kind of bond between atoms, the ionic bond. Ions can be created when an electron is lost, for instance due to the impact of radiation, or when a strongly charged nucleus approaches a more-weakly charged one. In this case, the positive charge of one nucleus overwhelms the positive charge of the other, forcing a transfer of electrons to balance things out, and both become ions. Since one ion is positive and the other negative, the atoms are pulled together. However, as the atoms approach their electrons are drawn into the space between their nuclei and they create covalent bonds as well. Ionic bonds often form between metallic and non-metallic elements – an example being table salt, which is a compound of sodium (a metal) and chlorine (a non-metal).

The details of how and why atoms combine to form molecules, and how molecules interact with one another and otherwise behave, is the subject of chemistry, and some of its discoveries are needed to explain the properties of water. For water is a compound, its molecules comprising one atom of oxygen and two of hydrogen, which is why its chemical formula is H2O. These atoms have covalent bonds between them, with one hydrogen atom on either side of the oxygen atom. Each hydrogen atom brings with it one orbiting electron, and each oxygen atom brings six. In the covalent bond of the water molecule, the single electron of the hydrogen atom is paired with one of the six electrons of the oxygen atom.


The distorted tetrahedral shape of a water molecule (redrawn after H2O: A Biography of Water by Philip Ball)

With two such bonds in each molecule, there are two hybrid pairs of electrons and two pairs of electrons that are not involved in the bonding. Thus the oxygen atom is surrounded by four electron pairs, all negatively charged. Since they repel each other, the pairs arrange themselves as far from each other as possible. All else being equal, this would create a four-pointed structure or tetrahedron, with a regular angle between each of the participants of 109°. But instead, because the two non-bonding electron pairs remain closer to the oxygen atom’s nucleus, these more strongly repel the two bonding pairs, thus pushing the two hydrogen atoms closer together. The result is a distorted tetrahedral arrangement in which the hydrogen-oxygen bond angle is only 104.5° (see the picture on page 9). Remember this diagram: it might be the most important shape you’ll ever see, for in it is contained the power to bond, to dissolve, to shape, to convey, and to transform.


Each water molecule, then, is an oxygen atom surrounded by four points, two of them, on one side, being hydrogen nuclei, and the other two, on the other side, being pairs of electrons. The hydrogen nuclei have a positive charge, since their electrons are closer to the oxygen nucleus than they are to their own hydrogen nucleus, while the electron pairs have a negative charge. This arrangement has two important, but linked, consequences. First, one side of the molecule is positively charged and the other negatively charged, making the water molecule polar. This means that the positive side of a water molecule is weakly attracted to the negative sides of other water molecules, and vice versa, and that they are also attracted to their opposites in any other polar molecule that they meet.

Not all molecules are polar but many are, because they have a net positive and a net negative part, side or end. They include molecules with a hydrogen-oxygen group at one end (for instance some sugars, like glucose, and alcohols, such as the ethanol in alcoholic drinks), and molecules with a hydrogen, oxygen or nitrogen atom at one end (like water itself, and ammonia, and many biomolecules or parts of them). All of these have a mutual attraction to water, so are called hydrophilic, and the smaller ones all dissolve in water. The same applies to most compounds with ionic bonds, since the negative–positive attraction that holds them together can be switched to water as they dissolve in it. Shapes of stable, highly structured water molecules are created around each polar molecule or ion. These are called hydration shells, and are like moulds or negative images of the substance that water has encountered. Some believe that these hydration shells can persist even after the substance that made them has departed, suggesting that water may have some kind of ‘memory’.

One result of its polarity is that water is an excellent solvent, so it can pick up and carry many other kinds of substance. Another is that it can help organise complex biological molecules, for instance in a cell, by attracting those parts of large molecules that are hydrophilic, and repelling other parts that are non-polar and hence hydrophobic. Cell membranes, for example, are made of layers of phospholipids (phosphorus compounds attached to fats or oils), and in a watery environment the hydrophobic oily ends hide away inside the membranes, making the whole structure possible. So too, all-important protein molecules often depend on their shape to have their proper function, and rely on the presence of water to guide their hydrophilic and hydrophobic sections into the right places. Without water, these biomolecules would unravel and cease to function, and many require bondings with a very specific directionality that only water can provide.

The watery environment can hold many molecules and ultrafine particles in suspension, forming what are called colloids, with their own unique properties. Notably, such water-based colloids can easily be transformed from a fluid or sol state into a semi-solid gel state, and back again: transitions that underlie many cellular mechanisms. As Philip Ball put it in his book H2O: A Biography of Water: ‘That the only solvent with the refinement needed for nature’s most intimate machinations happens to be the one that covers two thirds of our planet is surely something to take away and marvel at.’

The other consequence of the twisted tetrahedron is that each water molecule is able to form four hydrogen bonds with other molecules, positive (water’s two hydrogen atoms) to negative parts of other molecules, and negative (water’s two lone electron pairs) to positive parts of other molecules. These hydrogen bonds (H-bonds) are about ten times stronger than the forces of attraction between polar molecules, but about ten times weaker than the covalent bonds between atoms. They are, however, strong enough to make water molecules decidedly ‘sticky’, and it is these hydrogen bonds that dominate the structure of water. In liquid water, then, every molecule spends most of its time H-bonded in all directions.

This is not a static arrangement, though, as the molecules switch H-bonds very rapidly, in trillionths of seconds. So the whole thing is both highly structured, being a single, huge H-bonded cluster, and also highly dynamic, since H-bonds break and re-form with lightning speed. There’s also some kind of co-operation involved, because the forming or breaking of one H-bond alters the chance that another will be made or broken nearby. Why or how this happens is one of the mysteries that surround water, while at a practical level making it very hard to describe or model the structure of liquid water.

Although water molecules are unique in being able to form as many as four H-bonds each, this form of bonding is not exclusive to water. Any molecule that has a hydrogen atom attached to an oxygen or nitrogen atom is capable of H-bonding. This includes alcohols such as butanol and ethanol (which are also polar molecules), which contain groups of oxygen and hydrogen atoms, and other carbon-based (or organic) molecules that have groups of nitrogen and hydrogen atoms. These range from simple molecules like methylamine to large ones like proteins and DNA. Hydrogen bonds help biological molecules form and maintain their proper shapes, including the DNA double helix, the two strands of which are held together by H-bonds between hydrogen atoms attached to nitrogen atoms on one strand, and lone electron pairs on another nitrogen or oxygen atom on the other strand. The net effect is that a firm but breakable chain of H-bonds links the helices together, until they need to be ‘unzipped’ to allow them to be read into RNA or copied into DNA, thus allowing the chemistry of life and heredity to occur.


As heat energy is fed into a liquid, its molecules bounce around with increasing vigour. Eventually they vibrate so hard and fast that they start losing contact with one another, and the liquid boils away into a vapour or gas. This boiling point depends on pressure as well as temperature, since high pressure holds the molecules together in a liquid form up to a higher temperature than at low pressure. This is why ‘the’ boiling point of water is always described as 100°C at sea level, i.e. under one Earth atmosphere of pressure. If you increase this, for instance by heating water in a pressure-cooker or autoclave, it will be superheated to much more than 100°C before boiling. But if you heat water at a high altitude, under low pressure, it will boil at a much lower temperature than 100°C, making it hard to make a decent cup of tea.

Pressure is not the only thing that holds molecules together, though. Another is hydrogen bonding. The boiling point of a liquid ought to be roughly related to the size of its molecules, with small ones bouncing around more at lower temperatures than large ones because of their lower mass and weaker bonding forces. By comparison with other liquids made of molecules of about the same size, such as methane and hydrogen sulphide, water would be expected to boil at about minus 90°C, not plus 100. Other liquids with H-bonding, such as hydrogen fluoride, ammonia and ethanol, show the same anomalously high boiling points, though not as strongly. Without H-bonds, water would exist in our world solely as a vapour, creating a grossly amplified greenhouse atmosphere and a surface temperature of hundreds of degrees, rather like Venus where the air is hot enough to melt lead. But instead, on Earth, water has existed as a liquid for almost all the time and in almost all places over the last several billion years.

The temperature rise in a substance caused by a certain amount of heat energy being put into it is called its heat capacity. This is extremely high in water, because of its structure, so more heat is needed to raise its temperature than almost any other substance, and more heat has to be lost to cool it down. This means that blood can carry heat away easily from working muscles and other hot organs, helping to keep the whole body at an even temperature of 37°C. It also means that ocean currents can carry phenomenal amounts of heat, ensuring that the world as a whole is kept at a relatively constant temperature. Without water’s high heat capacity, the Earth may well have been uninhabitable, except possibly in patches.

Related to its heat capacity, water also has a very high latent heat, which is the heat energy absorbed by a substance as it changes from liquid to vapour, or released when it changes back again. Thus, lots of heat is taken up when water evaporates on the skin, making sweating an effective way to cool the body down. Water also conducts heat unusually quickly, again helping bodies to stay evenly hot, although it can make scuba diving in cold water very chilly, and diving near volcanic vents very dangerous.

Liquid water has unusually strong surface tension, since the H-bonds hold the surface molecules together in a skin, upon which all manner of small animals can run (like water skaters) or dangle (like mosquito larvae). High surface tension also allows capillary action, by which water creeps upwards in small spaces, for example raising underground water through the soil to the roots of plants, and then internally upwards to their leaves. By tugging at solid surfaces, it also helps erode rocks into tiny particles of silt, from which chemicals can more easily be dissolved, thus helping to create soils, and bearing nutrients through ecosystems.


Like other substances, liquid water contracts and becomes denser as it cools. Cold surface water encounters air and dissolves oxygen, so by sinking it delivers oxygen to deep water, where it supports life that would otherwise suffocate. Also like other substances, water expands as it’s warmed, but while most liquids do all this expanding and contracting from the moment they melt, fresh water only does it from 4°C. From that point it expands whether you heat it or cool it. The cooling expansion is due to the H-bonded molecules forming large clusters, which push them apart. But the system is transformed when it freezes, since the H-bonded molecules suddenly enter a new hexagonal lattice formation, which is about 9 per cent bulkier than cold liquid water.

A 9 per cent expansion on freezing makes water truly unique, since other substances become denser when they freeze, and the fact that ice floats on liquid water has awesome consequences for life. Taken together with the density maximum at 4°C, which makes cold water sink, it means that the cooling of a fresh water body such as a lake or pond isn’t just a surface event – the whole thing has to be around 4° before any freezing can happen. Then freezing only occurs from the top down, and usually stops when there’s a layer of ice floating on the surface. Hence the deeper waters remain liquid, at 4°C, and fish and other organisms can survive there throughout the winter. This is slightly different for sea water, since its salt content lowers the freezing point by about 2°C, and also lowers the temperature of the density maximum. The effect of this on sea water is to make the deep waters of cold oceans like the Arctic about 4°C colder than the depths of frozen-over fresh waters. This is a physiological challenge for Arctic fish, many of which have antifreeze molecules in their blood to cope with zero-degree water. But ice does float on both sea water and fresh water, which is fortunate since otherwise ice would sink like stone, filling up the bottoms of the oceans and lakes far from the warming sunlight of spring. In other words, the world’s water bodies would quickly become solid ice, with a seasonal layer of liquid water on top.


The list of other water anomalies is a long one, over sixty at the last count, and all are probably connected one way or another to its exceptional H-bonded structure. Strangenesses include those to do with temperature, with cold liquid water shrinking as it’s heated, becoming harder to compress, easier to heat, less able to dissolve gases, slowing light more and sound less, and hot water doing the exact opposite on all counts. Meanwhile, with increasing pressure, cold water molecules move faster and the water becomes more runny, but hot water molecules move more slowly and the water becomes more viscous. Finally, no other material is commonly found as solid, liquid and gas, with local and seasonal transitions between these forms driving most if not all of the world’s ecology.

Did I say finally? I meant, until we look at ice again. This, it turns out, comes in a dozen different kinds, depending on pressure. Regular ice at low pressure, i.e. from below one atmosphere up to a thousand or so, is made of hexagonal structures of H-bonded molecules, with plenty of space inside. But increase the pressure and you start to see the molecules slip suddenly into new configurations. Two new forms happen between 1,000 and 3,500 atmospheres, and another three (one of which can only fleetingly exist) between 3,500 and 20,000 atmospheres. The first four of these are all more-or-less deformed versions of the regular ice H-bonding matrix, but the fifth, and two others that form above 20,000 atmospheres of pressure, are organised in interlocking networks, packing more than twice the number of molecules into the same space, while at even more extreme pressures the hydrogen bonds themselves are completely reinvented. Not surprisingly, these various forms of ice behave in odd ways that physicists find fun, with one form having a melting point of 80°C and another of over 100°C, but only if they are kept under pressure. This is fortunate for life, since ice that melted only at that kind of temperature would be lethal if it got out of the laboratory and spread.

There are interesting things to find at very low temperatures too, even outside super-pressure chambers. If you condense water vapour quickly on an ultracold surface, you get a kind of fluid ice that’s as viscous as molten glass, which survives from minus 120°C to minus 140°C. But then, if you put regular ice under 10,000 atmospheres of pressure at minus 196°C you get another kind of glasslike ice, and at several thousand atmospheres and temperatures below minus 75°C, there may be two kinds of liquid water as well. This all seems to show water seeking the best possible configuration and bonding pattern among its molecules to reconcile contradictions in the energy environment that experimenters have created. This sort of responsiveness and adaptation is almost lifelike, and makes one wonder anew about what water actually is.


Returning to regular ice, the mysteries aren’t over yet as we haven’t looked at snowflakes. These little crystals are famous for their unique shapes, many of them very beautiful. They form in certain conditions of moist, cold air, but in other conditions the ice can make plates, needles, prisms and other shapes instead. The classic snowflake grows identical fern-like tendrils along paths that diverge at 60° because of the hexagonal arrangement of molecules in ice. They show an extraordinary, inexhaustible creativity of form, and no other substance crystallises in so many different shapes. But the big question is why are snowflakes symmetrical, with every branch identical to every other? It’s as if each of the six branches somehow knows what the others are doing, and does the same. There are two main hypotheses to explain this. One is that all the branches are similar because they happen to grow close together under the same conditions at the same rate. The other is that there are vibrations in the crystal lattice of the growing ice, which bounce back and forth through the crystal, thus organising it. The first idea sounds weak, while the second begs the question of what kind of vibration in what kind of field could achieve this? Rupert Sheldrake, an eminent biologist, neatly incorporates snowflake symmetry into his theory of morphic resonance, envisioning morphogenetic fields that organise growth and form in everything. Maybe so, but that’s another story.


By now it should be clear that water is a simple thing, but also very complicated. And there’s one final, final thing. When we drink water, we sense that there’s something different between a scoop from a mountain spring and a mouthful taken from a bottle of well water, or a glass fresh from the tap and one that’s been standing overnight. There are all sorts of ways in which these waters may differ, including all manner of dissolved chemicals, but there’s also a feeling of energy and liveliness that varies. Fresh spring water has a buzz to it that dead river water doesn’t possess. This is hard for chemists to analyse, but people feel it anyway.

Water is inherently dynamic: it stores and responds to energy. We’ve seen how the great complexes of water molecules seethe with breaking and re-forming hydrogen bonds, billions in every instant, and all this activity alters radically with temperature and dissolved salts and gases as the ever-changing labyrinth of molecular bonds responds to minute signals. Many of the molecules in liquid water are fragmented into hydrogen (H+) ions and hydroxide (OH-) ions, and the proportion can vary hugely with light, heat and dissolved materials. Adding even a little acid increases the number of hydrogen ions, while adding any kind of base increases the number of hydroxide ions. Meanwhile, hydrogen ions can ‘move’ almost instantly along chains of linked water molecules – if one is added at one end of a chain, another appears at the other end, as if by magic. By putting a sample of this extraordinary substance in our mouths, it’s hardly surprising that we can sense its condition, somewhere in the vast range of energy states that water can adopt, and feel the way it instantly changes in response to new conditions even as it touches our lips.



Water in the Biosphere


THE BIOSPHERE IS the name we give to all the parts of the Earth where life occurs, the maximum extent of all ecosystems. Water exists throughout the biosphere, inside living organisms, and as ice, vapour or liquid throughout their environments. There are about 1.4 billion cubic kilometres (km3) of water on Earth, of which almost all is sea water. Of the 36 million km3 of fresh water, two-thirds is frozen in ice caps and glaciers, and only about 12 million km3 is liquid, almost all of which is held underground in rocky aquifers. The remaining 200,000 km3 or so are found above ground, or nearly so. Of this watery fraction, some 90,000 km3 comprise lakes, 90,000 km3 are in soils and permafrost, 13,000 km3 are in the form of atmospheric water vapour, 11,000 km3 are in swamps, 2,000 km3 are flowing in rivers, and 1,000 km3 are inside living organisms.

All these figures are very approximate, and prone to change as new discoveries are made – such as on the size of aquifers and the amount of water bound into deep rocks – and as climate changes increase the melting of permafrost, ice caps and glaciers. The general pattern of water in the biosphere, though, is that it moves through two kinds of cycle. There is a slow cycle, in which water is held for millennia in aquifers and in long-term ice, only gradually seeping onto the surface through springs, or streams from melting glaciers. Then there is a fast cycle, in which about 500,000 km3 of water evaporates every year from sea and land, becoming vapour that condenses to clouds and falls as rain. It is this fast cycle that irrigates the dynamic parts of the biosphere on land. The other parts, the spores and seeds trapped in long-term ice, are best described as still life.

The largest volume of the biosphere is gas, our atmosphere, which is inhabited to great heights by tiny spiders drifting on silken threads, by the spores of bacteria, fungi, ferns, lichens, mosses and other organisms, and by the lightest of wind-dispersed seeds and pollen grains. These push the upper limit of the biosphere up to an altitude of at least 17 km, which is about the extent of the upper limit of the troposphere at the equator. This inner layer of the atmosphere is constantly mixed by rising air, but at its top it gives way to the jet streams and the stratosphere above them. At lower levels, we find birds typically flying from near ground level to a height of about 2,000 metres, but some go much higher. Bar-headed geese migrate over the Himalayas at 8,300 metres, and have been seen above that. In 1973, a Rüppell’s griffon vulture collided with a commercial aircraft over Abidjan, Côte d’Ivoire, at a height of 11,280 metres. At such an altitude, more than 90 per cent of the mass of the atmosphere lies below the bird’s wings, and temperatures are around minus 50°C. Such high-flying birds, which also include turkey vultures, buzzards, ospreys, terns and cranes, occasionally go into the upper troposphere and ride jet streams there.

Life becomes far denser within the biosphere close to, on, and just beneath the Earth’s surface, where all its key resources come together. These include the sunlight and warm dense gases of the lower atmosphere, which may also be dissolved in water to sustain aquatic life. In particular, there is oxygen to support aerobic respiration, and carbon dioxide for photosynthesis. There is also nitrogen, the air’s commonest ingredient, which is fixed as nitrates by soil and root bacteria. The resources of the planet’s surface also include the trace nutrients and minerals needed by plants and animals. Examples include magnesium, a component of chlorophyll which traps sunlight in plants, and iron, part of the haemoglobin molecule which transports oxygen in mammals. Thus, on land there is the familiar bustle of vertebrate and invertebrate animals and plants, the burrows and roots of which penetrate tens of metres into the soil. This life draws on resources of light, air and soil, but largely feeds on itself, obtaining most of the carbon, nitrogen, phosphorus and other elements it needs by recycling the dead and the wastes of the living.