How much water is in your burger?


  • Water is vital, but few are aware of how much water is needed to produce the food we eat. The impact of the virtual water concept is immense.
  • 1.7 billion people live in areas where groundwater resources and/or groundwater-dependent ecosystems are under threat.
  • Consumer habits and integrated water governance are pivotal for hydrologically sustainable food production.

Picture this:  You are in Sacramento – California, 1990. You have a large farm outside of the city that abstracts water from a borehole to irrigate crops and water your livestock. Since the water price is very low, the cost for irrigation is almost zero and as long as nobody regulates the withdrawal, it is your call to pump as much as you can. Throughout the years, your farm produces tons of rice, beef, apples and other crops. Your goods are sold directly in town and to food distributors. You make lots of money and many farms like yours do the same, well done.

Now, come back to 2020. The Sierra Nevada snowpack is barely half of the normal level and groundwater levels are at a record low causing land subsidence. Sacramento is in a region which is heavily threatened by climate change and desertification. What happened? Well, it is rather complicated. One piece of the puzzle may be the topic of this article: the agricultural water footprint. But let’s start from the beginning.

Until a hundred years ago, farmers had to rely on water pouring down from the sky. Ingenious ones used to store some of it in wells not to be caught unprepared during dry seasons, drought, natural disasters. But small wells and reservoirs could only do this much to fill the gap between the water actually available and crops’ demand for it. It was only with development of irrigated agriculture – that means by withdrawing “blue water” from the aquifers – that humanity could boost crop production and increase the yield per hectare, guaranteeing more and cheaper food. Such intensive irrigation, however, depletes groundwater resources. Aquifer levels keep going down and are currently being depleted faster than they are recharged by the rain. Desertification is encroaching farmland and settlements with massive implications for the respective communities. In less than a century, water availability has become an issue of increasing concern and the science of hydrology has become an important field of study. Freshwater demand for personal and productive use over the next decades is rather incompatible with the limited volume available in many places. Water sources are already overexploited, which is an issue that ultimately undermines not only developing countries but global food security. As a result, it is ever more important to optimise the way freshwater is utilised in agriculture and to define strategies to manage water as a precious resource and not as an infinite, wasted for nothing, commodity.

A graphic metric to understand the scope of the problem is the so-called groundwater footprint. The most overexploited aquifers are located in Asia and North America. They are the backbones of the drinking water supply and have shouldered the bread-baskets and subsequent rise of the population of the respective regions. Figure 1 communicates the size of aquifers that is necessary to sustain current groundwater use and dependent ecosystem services of a given aquifer. For example, in the upper Ganges, the aquifer would have to be ~25 times as big as it actually is to sustain current extraction levels and existing ecosystem services. All in all, the current groundwater footprint is about 3.5 times the actual area of aquifers with 1.7 billion people living “in areas where groundwater resources and/or groundwater-dependent ecosystems are under threat” (Gleeson et al., 2012).

Groundwater Footprint Map from Gleeson et al. (2012)
Figure 1 Groundwater Footprint Map from Gleeson et al. (2012)

Despite being only one of the many ways to calculate the water footprint, the virtual water concept has received much attention from the academic community and the broader public, as it helps to understand the volume of water involved in the production of a good. Virtual water is expressed in water volume per unit of product (m3/ton) and is considered an interesting tool to assess how the production of a good affects the freshwater availability in different regions. Some examples: it takes some 280 litres of water to produce 1kg of potatoes, 1020 litres to produce just one litre of milk, nearly 5000 litres for a kg of pork and more than 15000 litres for a kg of beef. Some other examples are available here. Evidently, water is caught in the tragedy of commons as it is easily spoilt and used by individual users, disregarding negative externalities, which arise from the respective productive activity and that affects the entire community, Groundwater used for irrigation, as in the introductory example, is a classic example of this tragedy.

According to Hoekstra, the total consumption of freshwater can be split into three types: green, blue and grey. Bluewater refers to the volume of surface and groundwater consumed, the green water footprint refers to the rainwater consumed and greywater is the freshwater that assimilates pollutants and is therefore polluted. This classification is a useful starting point for countries suffering water scarcity to define strategies to better manage their limited water resources, including improved farming techniques, grey-water-reuse and import of water-intensive goods rather than domestic production. By paying an uncharge for the cost of importing such goods, these countries would arguably unload the environmental and social burden to the exporting countries. Yet, context matters. Saudi Arabia’s wheat experiment, for example, stands out as one of the least sustainable endeavours for water management. The country, one of the world’s wealthiest, decided to evaporate its unreplenishable fossil groundwater evaporate in the desert – for a few extra bucks, compared to its oil margins.

Wheat fields in Saudi Arabia
Figure 2 Wheat fields in Saudi Arabia

If for some countries, the use of groundwater is not a choice – it is estimated that in 2025 there will be 1.8 billion people living in regions with absolute water scarcity. Developed countries’ consumption habits and domestic agriculture have a big responsibility in this. Take, once again, the United States: crops irrigation has accounted for at least 80% of total water withdrawals in the western United States. In the future, a growing population and rising incomes will further increase the demand for water, also in non-agricultural sectors and for luxury goods.

So which products are important and which ones are not? What foods do we want to eat, knowing they potentially slowly drain unique ecosystems? Which goods are water demanding and which ones are not? Popularising the virtual water footprint can help fathom the answers to these questions. Consumers can make conscious choices and stakeholders can formulate strategies that keep such information visible and producers accountable. You and I can aspire to consume goods and services which are produced with hydrological sustainability in mind. By the way, next time you are eating that delicious burger, bear in mind you are holding over 2000 litres of virtual water in your hands.

Alessandro is an environmental engineer and project manager. He lives in London and is passionate about the way we can change things with the help of data and technology.

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