Although oceans cover about 70 percent of the earth’s surface, water is nonetheless a scarce commodity — at least freshwater, which after all represents only three percent of the world’s water reserves. And most of that water is frozen in the polar ice caps; compared to the salt water of our planet’s seas — about 1.3 billion cubic kilometers — the roughly 200,000 cubic kilometers of water in the world’s lakes and rivers are like a pathetic trickle. Only less than 1% of global water supplies can be used untreated by humans.

The most abundant freshwater reserves are found in groundwater, but half of it is more than 800 meters underground. And in places where such deep drilling isn’t necessary, there is the threat of a falling water table.   Thereby each person on earth needs 20 to 50 litres daily for their basic needs. Water scarcity is a severe problem that is now having an impact on more than 50 countries; people in arid regions of Africa must make do with just 20 liters per person, per day. The largest share of annual rainfall comes down in the space of a few days — the rest of the year remains in the grip of drought.

 This is why the biggest share of our freshwater ends up on cultivated fields. Approximately one billion people of the total world population of 6.8 billion don’t have access to clean drinking water. And for two billion, access to sanitary facilities is an absolute luxury. On average, 4,500 children die every day from infections caused by unclean water. And the situation is becoming more dire: environmental pollution, climate change, and springs that are drying up will make the precious liquid as expensive in coming decades as petroleum is today.

In Germany people use about 125 litres of water daily. Only 3 to 6 litre of that is needed for drinking and cooking. Most of the water is used for flushing the toilet, taking a bath or shower.

In future water will become and even scarcer resource. That is the conclusion drawn by the 2009 Unesco water report with the title “Water in a changing world”. The causes are the needs of the world population growing by 80 million people per year and the effects of climate change.
Most water - approximately 70% of worldwide consumption - is used for food production. However, around half the water used in agricultural irrigation can be saved by implementing more efficient irrigation methods.

“Virtual water”

The British scientist John Anthony Allan created the term “virtual water”. It stands for hidden quantities of water, though not contained in products but used in its production. Allan determined that each cup of coffee contains 140 litres “virtual water” used for cultivation, production, packaging and shipping of the beans. According to this research model a meat burger contains 2,400 litres “virtual water”. According to Allan’s research model a US citizen uses 2,400 litres “virtual water” per day, while a German citizen uses about 4,000 litres per day.

Astonishing facts about the use of “virtual water”:

• 550 litres of water are needed to produce 400 grams of flour.
• 1,000 litres water is needed to produce 1 litre of milk.
• Water consumption for the production of 1 kilogram of...
  • Rice: 3,000 litres
  • Maize: 900 litres
  • Wheat:  1,350 litres
  • Beef: 16,000 litres
    
    

Source: “100 facts and figures on the topic water.” - German IHP/HWRP national committee at the Federal Institute of Hydrology (BfG)
http://ihp.bafg.de/servlet/is/8397/