The water footprint was first developed in 2002, offering a measure of the total water used to produce a given product, from supply chains to the point of purchase. Some consumers may wish to use it to guide purchase choices, but while useful for raising awareness, it is important to be aware of its limitations, with the potential to promote choices which may not be in the best interests of the farms and countries of origin.
Since 2010, ‘water footprint’ as a concept has become widely used throughout industry, in particular towards consumers. The concept derives from ‘virtual water’ developed by Tony Allan, 2003 – the principle of which is that while a product may itself contain little or no water, very often its growth or production requires large amounts of water in another country from where it is purchased and consumed.
Professor Arjun Hoekstra and his colleagues at the University of Twente, Netherlands, progressed this work into developing a water footprint calculation method, which has proved highly successful in further raising awareness of the international impacts of our consumer choices.
The impacts are most significant for agricultural produce for food or textiles. A commonly quoted example is that 1 cup of coffee (about 125 ml) has a water footprint of 140 liters (Chapagain and Hoekstra, 2003).
Most of this represents the water used in growing the coffee plant and beans, but also includes water used in processing the beans, and filtering the coffee. How is this water volume calculated?
Does 1 cup of coffee really equal 140 liters of water?
A growing plant takes up water from the soil via its roots bringing with it essential minerals and nutrients. Most of this water eventually departs from the plant as transpiration from its leaves, at varying rates depending on the time of day, weather conditions, season and plant maturity. The idea is that when you drink your 125ml of coffee, you should be aware that you have also ‘used up’ 140 liters of water somewhere else in the world, and perhaps in a region of water scarcity.
Allan, JA, 2003. Virtual water – the water, food and trade nexus: Useful concept or misleading metaphor? Water International, vol 28, no.1, pp 106-113.
Chapagain, A.K. & Hoekstra, A.Y., 2003. The water needed to have the Dutch drink coffee, UNESCO-IHE, Value of water research report no. 14, 40pp.
Deurer, M., Green, S.R., Clothier, B.E., Mowat, A., 2011. Can product water footprints indicate the hydrological impact of primary production?–A case study of New Zealand kiwifruit. J. Hydrol. 408 (2011), 246–256.
Hoekstra, AY, Chapagain, AK, Aldaya, MM & Mekonnen, MM, 2011, The water footprint assessment manual – Setting the global standard, Earthscan, 228pp
Keys PW, Wang-Erlandsson L, Gordon LJ ,2016, Revealing Invisible Water: Moisture Recycling as an Ecosystem Service. PLoS ONE 11(3): e0151993. doi:10.1371/journal.pone.0151993
Mekonnen, MM & Hoekstra, AY, 2011, The green, blue and grey water footprint of crops and derived crop products, Hydrology and Earth Systems Sciences, 15, 1577–1600, 2011
Perry, C, 2013, Water footprints: Path to enlightenment or false trail? Agricultural Water Management 134 (2014) 119– 125