Water footprints at Higher Level: This statement is Higher Level only. It applies the footprint idea from 1.3 to water: how much water lies behind what we eat, wear and buy, and how that guides decisions about water security.
Practise this as you read
- Split a footprint into green, blue and grey water.
- Judge whether a footprint is sustainable.
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All the water behind what we use: Most of the water you use is invisible: it was used to grow your food and make your clothes. A water footprint counts all of it.
The points to remember
- A water footprint measures all the freshwater used by a person, a nation or to make a product.
- It counts direct use (taps, showers) and indirect use: the water hidden in food and goods.
- Green water: rain used by crops. Blue water: river, lake or groundwater used.
- Grey water: the water needed to dilute the pollution made.
- It is given in litres or cubic metres (1 m3 = 1,000 litres) per person, per year or per product.
Remember it as: Green from rain, blue from rivers, grey to clean up.
Real example: the Water Footprint Network works out that the average person in the world has a footprint of about 1,385 cubic metres a year: almost 4,000 litres a day, far more than anyone drinks or washes with.
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Every product has a footprint: the water used at every step, from the field to the shop. The guide lists crops, livestock, textiles and steel.
Products
- Products made from animals have the biggest footprints: animals eat crops that need water.
- 1 kg of beef needs about 15,400 litres; 1 kg of chicken about 4,300.
- A cup of coffee needs about 130 litres, mostly to grow the beans.
- Cotton clothes need a lot of irrigation water; synthetic fibres need less water but use oil.
- Farming is about 92% of humanity's water footprint.
Real example: California grows about 80% of the world's almonds, and each almond needs about 12 litres of water, much of it irrigation water in a state that suffers droughts.
Adding up everything a country's people consume gives its national footprint, usually shown per person so countries can be compared.
Nations
- The world average is about 1,385 m3 per person per year.
- The United States is about 2,842 m3: more meat, more goods, more irrigation.
- India (1,089) and China (1,071) are lower per person, but huge in total.
- A nation's footprint has an internal part (its own water) and an external part (imports).
- Importing food imports virtual water, used in the country that grew it.
Real example: the United Kingdom takes relatively little water from its own rivers, but much of its footprint is external: the water used abroad to grow its imported food, cotton and coffee.
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A footprint is a measure of sustainable use. It also shows decision-makers where the water goes, so it can guide water security.
Using footprints to decide
- Sustainable if the footprint is no bigger than the water that is renewed each year.
- Governments: decide which crops to grow and which to import, and where water is over-used.
- Companies: find the thirstiest step in their supply chain and cut it.
- Consumers: choose products with smaller footprints, such as chicken instead of beef.
- Limits: an average hides where the water came from; a litre in a wet place matters less than in a dry one.
- Limits: green water does less harm than blue; grey water is only an estimate.
Footprints help
- Show hidden water in food and goods
- Compare people, nations, products
- Guide crop, import and buying choices
But
- Averages hide where water came from
- Green and blue water count the same
- Grey water is only an estimate
Real example: a kilogram of avocados grown with irrigation in dry central Chile puts far more pressure on local rivers than the same footprint from rain-fed farms in a wet region: the number is the same, the harm is not.
How this comes up: Paper 2, Section B (b): explain how water footprints measure sustainability and inform decisions [7].
The average person in the United States has a water footprint of about 2,842 cubic metres a year, twice the world average.
Explain how water footprints can be used to assess sustainable water use and to inform decisions about water security.
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