3. Water Footprint
3.1 What is a Water Footprint?
The concept of a water footprint was developed in 2002 by Arjen Hoekstra, a water management scientist working for UNESCO-IHE Institute for Water Education. It was created as a way to measure the amount of water used and polluted along the entire supply chain of a good or service. It built on the idea of virtual water but is more encompassing because it includes all water used, both direct and indirect water.
This concept can be applied at different scales. For example, the water footprint of a box of apples can be discussed, which would include all the water that goes into growing the apples themselves but also the water needed for the manufacturing of the box and shipping of that box to the store, etc. At this small scale, the water footprint is not really different from just discussing the virtual water of a box of apples.
However, the concept of a water footprint can be applied more broadly too, such as to the water usage of an individual or the water usage of a country over a particular time range, typically a year. In the case of an individual, the water footprint would include all of the virtual water embedded in food eaten, in energy used to power appliances or other electronics, in fossil fuels used to operate a vehicle or take public transit, in all non-food goods purchased, etc. plus all of the direct water used for drinking, cooking, cleaning, watering gardens, and so on.
If you would like to see how your personal or family water footprint compares to others in the U.S., this website is an easy place to calculate it: https://www.watercalculator.org/wfc2/q/household/
Check your understanding: Influencing your water footprint
This problem is a bit more advanced and requires application of knowledge about how different actions change water usage and therefore affect water footprint. Drag and drop the actions from the right-hand side into the appropriate column based on whether that action would increase or decrease a person’s water footprint. *Look back at information and data from previous chapters to help if you need it!
3.2 Water Footprint Components
When a water footprint is analyzed, the water is separated into three components: green water, blue water, and grey water. This is a useful way to measure how and where water is being used to compare with other countries or industries, or to help determine where water savings could be made to increase water sustainability.
The green water footprint is water from precipitation, either rainwater or snow. This is water that becomes stored in the root zone of plants and then either taken up by the plant and incorporated into plant material or lost to evapotranspiration. Measures of green water are particularly important in agriculture and related industries such as horticulture and forestry.
The blue water footprint is water taken from either groundwater or surface water sources. In agriculture, all irrigation water would be blue water. Blue water would also be any water used for industrial purposes, water used in energy production, and water for domestic purposes, such as cooking, cleaning, and drinking.
The grey water footprint is a measure of how much water has to be used to dilute pollutants such that their discharge will meet water quality standards. Almost all aspects of growing crops, raising animals, mining raw materials, extracting fossil fuels, etc., and then turning those into useable forms generates pollutants which cannot be released back into water bodies without diluting them to acceptable concentrations again. Of the three components of a water footprint, accurately measuring grey water is the hardest.
How does the world use water?
Between 1996 and 2005, the global water footprint for all of humanity for agriculture, industry, and domestic use combined averaged 9087 billion cubic meters of water per year. Of this, 74% was green water, 11% was blue water, and 15% was grey water. Agricultural use was by far the largest user of water with 92% of the water footprint a result of agricultural activities. Industrial production was 4.4% and domestic use was 3.6% (Mekonnen and Hoekstra, 2011).
Check your understanding: Water footprint components
References
Mekonnen, M.M. and Hoekstra, A.Y. (2011) National water footprint accounts: the green, blue and grey water footprint of production and consumption, Value of Water Research Report Series No. 50, UNESCO-IHE, Delft, the Netherlands. https://www.waterfootprint.org/resources/Report50-NationalWaterFootprints-Vol1.pdf
