Setting the scene
Water is an essential resource, without drinking it for example we can only survive for a few days. It also has many significant uses for agriculture and industry. Water demand is rising due to increases in populations and our ever-increasing need.
When delivering courses, students are often surprised at the water footprint for some well known products, here are a few examples:
- A kilogram (kg) of beef requires around 15 thousand litres of water (93% green, 4% blue, 3% grey water footprint)
- A 250 ml glass of beer requires 74 litres of water (85% green, 6% blue, 9% grey)
- A kg of bread has a water footprint of 1680 litres (70% green, 19% blue, 11 grey)
- A kg of chicken has a water footprint of 4325 litres (82% green, 7% blue and 11% grey).
I will explain what ‘green’, ‘blue’ and ‘grey’ mean below.
I thought we could only footprint carbon?
The concept of a carbon footprint is one that has been around for many years, and the process is well known and understood. Essentially, a carbon and a water footprint are similar in that they are trying to determine the amount of a substance that is used along the life cycle of an entity.
A water footprint is a calculation of the quantity of water that is required to create the goods and services that we consume or use. It can, and has, been calculated for products as we saw above, but also for companies or even a country.
It is common for a water footprint to consider three components, these are:
- Green water footprint: this would be precipitation that falls onto the land and used by plants. Growing crops for agricultural purposes for example would have a significant contribution to this category.
- Blue water footprint: this is water that has been gained from sources of water from the ground or surface, it would therefore include water from aquifers, rivers and lakes. It could include water for agricultural irrigation or water used to make products, such as a soft drinks.
- Grey water footprint: this is the water that is needed to control pollution so a few examples would be a pipe from an industrial premises into a river of diffuse sources such as run-off.
The examples water footprints for food products above are broken down into these components. Looking at these three components together is useful as we can more closely analyse the sources and put in place mitigation measures to reduce consumption.
The use of water footprint
One area that I think a water footprint helps to create awareness of is the concept of virtual water (sometimes known as embodied water). Let’s look at an example.
That cup of coffee that you have just bought from a well known coffee shop chain probably contains somewhere around 500ml of hot water, so the water footprint of that coffee is only 500ml, right? Well, no there is a bit more to it than that!
As we do for other environmental issues, like greenhouse gases, we need to understand the amount of water that has gone into growing, processing and transporting the coffee. This water is virtual or embodied to the person who buys the cup of coffee. It is important to understand this as it gives a true picture of the water footprint rather than just measuring the water needed to make the drink. By the way, the water footprint of 125ml of coffee has been calculated to be 140 litres of water (so to put that in perspective for one cup of coffee it is 70 x 2 litre soft drink bottles full of water) – all for that one small cup of coffee!
The work that Levis have completed is interesting, particularly on how the water footprint can increase or decrease depending on consumer habitats in different parts of the world. It is also an example of how water use can be significant in the use phase of a product (rather than the supply phase, as we saw in the coffee example). Some interesting statistics from their LCA study on a pair of 501s is that:
- 68% (2,565 litres) of the total water footprint comes from cotton production.
- 23% (860 litres) of water is used for consumer care (so basically washing your prized 501s).
- On average US consumers use more water (1049 litres) to wash their jeans compared to those in China (679 litres) and UK/France (619 litres).
- Chinese consumers wear their jeans 3.9 times between washes (it is 2.3 times for US and 2.5 times for UK/France)
From the above stats then, by completing a water footprint it helps to focus the mind on the hotspots of water consumption. An example in the Levi’s case study is that if consumers in the UK/France, China and the US wore their jeans for 10 times before washing then on average there would be a saving of 75%, 61% and 77% respectively throughout the lifecycle of the jeans! This has got to be the key purpose of a water footprint, we shouldn’t just measure for the sake of knowing, interventions need to be made at the correct part of the lifecycle to reduce water use.
However as the Levi’s LCA study shows there are other environmental impacts associated with a pair of 501s such as the greenhouse gasses that are released, so we ideally need to consider the whole impact of a product to get a true picture of the impact. There is no point in making changes to one area that has a detrimental impact on another.
I don’t think water footprinting is quite as popular as carbon footprinting. However, gaining an idea of the amount of water used by a product, service or country is vital to developing a true understanding of environmental impact. Happy (water) footprinting!
John Binns BSc (Hons), MSc, MIEMA
With over 19 years’ experience working in environment management, John Binns BSc (Hons) MSc MIEMA is an experienced environmental tutor and consultant with knowledge of health and safety management.