A full bath for a cup of coffee

A bathtub full of water to make one cup of coffee – that’s 140 litres! It takes almost as much water to make one breakfast egg. Sheer nonsense? British geographer Anthony Allan has found otherwise. At the Stockholm World Water Week, he and the WWF (World Wide Fund for Nature) came up with an amazing calculation on water consumption.

Their calculation is not just about the one cup of water that is poured into the coffee machine, but the total amount of water that is needed to produce one cup of coffee. And this starts with the cultivation of the coffee plant, which has to be irrigated intensively. Water is also consumed in the transport and packaging of the coffee. If you add it all up, you arrive at the initially unbelievable 140 litres of water for a single cup.

But the calculation goes even further. A T-shirt contains 4,100 litres of water, a new car swallows around 400,000 litres. In this way, every German consumes around 4,000 litres of water per day. This includes water consumption such as drinking or washing as well as consumption in the manufacture of products. Each of us leaves such a water “footprint”, depending on how much water we personally consume. Because much of this consumed water is invisible, it is also called “virtual water”. According to this calculation, we take almost 30 full baths per day – purely virtual!

Aral Sea dried up

It was once the fourth largest lake on earth. But compared to its former size, the Aral Sea in Central Asia is now just a puddle surrounded by a barren desert landscape. The reason: huge cotton fields in Kazakhstan and Uzbekistan. Cotton cultivation in this dry region requires artificial irrigation. Since the 1930s, farmers have tapped the two large tributaries of the Aral Sea, the Amu-Darya and the Syr-Darya, and channelled the water to their fields. The result: the Aral Sea dried up more and more. As the amount of water decreased, the lake also became increasingly salty. This also had an impact on the animal kingdom: of the more than 30 fish species that once lived in the lake, only six are now found in the salty lake.

The tough battle for water

Long queues of people crowd in front of the wells in Zimbabwe’s capital Harare. Water is particularly scarce in the townships of the city of millions. Time and again there are fierce battles over the scarce commodity.

The nearly three million inhabitants of Harare need twice as much water as is available. Only wealthy citizens have access to their own wells; the poor are often dependent on aid organisations for supplies. A major problem is the pollution of the water. One of the city’s two reservoirs is so dirty that it can no longer supply drinking water. Because of the contaminated water, thousands of people already died of cholera in 2009. Harare’s inhabitants fear another outbreak of the disease. Because of the poor water supply, violence in Harare is increasing.

The situation in Harare is not an isolated case. Many developing countries in Africa, Asia or Latin America have the same problems. In total, more than one billion people on earth have too little or no clean drinking water. The growing world population and climate change will in all likelihood further aggravate the situation

Milking the fog

The Atacama Desert is the driest desert on earth. On its edge lies the northern Chilean city of Iquique – an Eldorado for fog experts. Because here the conditions for “milking” fog are dreamlike: High humidity and lots of wind.

Climatologists have stretched fine-meshed nets to collect the fine fog droplets. Small drops collect on them and fall into a collecting channel. This makes it easy to collect the moisture from the fog – in favourable places, as much as five litres per square metre per day. This can be used to obtain drinking water – which is extremely scarce in this dry region. Other low-rainfall regions with mountains near the coast could also collect drinking water in this way. However, it is questionable whether the method is suitable for combating future water emergencies. In such a case, “fog milking” would probably be more of a drop in the ocean.

Drinking water

Colourless, pure and cool, without odour 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 drinking water is right, it is constantly tested in the waterworks’ laboratory. In Germany, drinking water is the best controlled foodstuff.

Drinking water does not bubble out of the tap by itself. It must first be treated so that it meets the high quality requirements. Groundwater is best suited for the production of drinking water. Because by seeping into the ground, the rainwater is pre-cleaned, as if by a filter. Pollutants and turbidity that are still in the water afterwards remain trapped in the filters of the waterworks. The clean water can finally be sent on its journey 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 groundwater. In addition, seawater must first be desalinated at great expense before it can be drunk.

The unequal distribution of drinking water

Turn on the tap and fill it with clean drinking water: It’s not as easy as it is here on earth. Although our planet is largely covered by water, there is a water shortage in many regions of the world. Even today, more than one billion people 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 kilometres to the next river or well. But there is also a water shortage where fresh water is contaminated by bacteria. The countries affected often lack the money to purify the water in sewage treatment plants as we do or to desalinate seawater.

Water consumption varies greatly in the different regions of the world. The industrialised nations consume much more water than the developing countries. When it comes to water consumption, it is not only water for drinking and washing that is important. Where there is a lot of consumption, the “virtual water consumption” is also the highest. This is because much more water is used in the manufacture of products than is apparent at first glance. This invisible water that is consumed 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 water are decisive reasons for the dwindling supplies. But global warming is also likely to exacerbate the unequal distribution of water. In regions where flooding is already a regular occurrence, rainfall will increase. And very dry areas will probably receive even less rain.

What water can do

No matter whether we drink tap water, jump into a lake or are surprised by a downpour – we constantly come into contact with water. And not only that: we ourselves are made of water, in fact about two-thirds of it. Without question, water is part of our everyday life. But what seems quite normal to us has all kinds of peculiarities. And water owes these above all 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 compound of two hydrogen atoms and one oxygen atom. These combine to form a water molecule, or H2O for short. The individual water molecules are only loosely connected to each other.

This loose cohesion ensures that the bond between the molecules breaks down at high temperatures: the water evaporates. If, on the other hand, it cools down strongly, the molecules arrange themselves into a solid, regular lattice, the ice. The special thing about it: In solid form, water has a larger volume than in liquid form.

The arrangement of the water molecules provides yet another property: the surface tension of the water. Because of this tension, water spiders and water striders can walk effortlessly 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.

The fact that lemons ripen on the island of Mainau on Lake Constance is thanks to another ability of water: it can store heat. Lakes or seas heat up in summer and retain the heat for a long time. That is why temperatures fluctuate less on the coast 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.