A water footprint is a measure of how much water your business uses and which direct and indirect environmental impacts result from this. It can help you understand and manage your water use and even protect your company from physical, regulatory and reputation risks. In this second article: choosing the best water footprinting method for you.
How do I choose a water footprinting method?
As we explained in part 1 of this series, water footprinting is a good way to manage your water-related risks and performance. Water is an essential resource that will only increase in importance, for the world and for companies. But how do you do a water footprint if there are so many methods to choose from? If you are new to water footprinting, the range of options can be overwhelming.
In SimaPro, 10 methods are available, each with their unique qualities. Some important considerations:
- Study objectives
- Acceptable level of uncertainty
First, of course, you must understand the differences between the methods. One good resource for understanding these methods is the SimaPro methods manual. In this article, we will illustrate the differences with some flow charts, although these cannot give an exhaustive overview. After this article points you in a certain direction, I suggest you read more about the methods that sound interesting before making a decision.
Midpoint vs endpoint
As with many life cycle impact assessment (LCIA) methods, there are two different types of water footprinting methods you can choose from: midpoint and endpoint methods. Midpoint methods apply a characterization factor to measure impact, while endpoint methods take this one step further and apply an indicator to express actual damages.
In the case of water footprinting methods, the midpoint methods measure local water scarcity and are typically measured in cubic meters of water. This number can be interpreted as the amount of water downstream users are lacking as a function of water consumption. An endpoint method measures damages and is often measured in DALY (Disability-adjusted life year) for human health impact. Some of the methods also include the damages on ecosystems.
Breakdown of midpoint methods
A key difference between the midpoint methods are the scarcity equations used. There are three main scarcity equations:
- Withdrawal to availability ratio (WTA) measures how much water in an area is withdrawn in the industrial process versus how much is available.
- Consumption to availability ratio (CTA) is similar to WTA, but takes into account that a lot of water can be withdrawn and then put back into the water source, for instance cooling water. Therefore, this method only includes water that is no longer available as a result of the process.
- Demand to availability ratio (DTA) includes human and ecosystem demand for water. This method examines the total amount of water available and subtracts the demand to see how much water is available for use.
The demand-to-availability ratio is unique to the newest water footprinting method in SimaPro: the AWARE method (Available WAter Remaining). This method was developed by WULCA (working group under the umbrella of UNEP-SETAC Life Cycle Initiative) in 2016 and was led by a few of the authors of the existing methods (Boulay and Pfister).
AWARE offers one generic impact category indicator for water scarcity, without necessarily being located at any specific point on the cause-effect chain of either the human health or the ecosystem quality endpoint indicator. This simplified method is excellent for LCA practitioners who need just one simple indicator.
All of the midpoint methods have m3 as the unit, except one: the Ecological Scarcity 2006 method, which is measured in environmental loading points. Similarly, all the methods (except Hoekstra et al 2012) use the WaterGap model to model water withdrawals and use. However, it is important to note that even though the different methods express their results in the same units, it is not possible to directly compare their results. If you choose a water footprinting method for one of your products, it is good to use it for your other products as well.
Breakdown of endpoint methods
The endpoint methods can also be broken down by what is included. Like the midpoint methods, they use different scarcity equations. As discussed, endpoint methods express their results in actual damages. Some only include human health impact, while the methods by Pfister include impacts on human health, ecosystems and resources and are also compatible with other existing methods (like Eco-indicator 99 and ReCiPe). The methods that only look at human health impact, however, are more comprehensive because they include more types of water use (domestic and fisheries in addition to agriculture), while Pfister only includes impacts caused by agricultural uses.
If you would like more information before choosing any of the methods, check out the descriptions of each method in SimaPro or the publications themselves.
Get started with water footprinting today
We hope this overview has helped demystify the key differences between the available water footprinting methods. With this information, you are better equipped to choose the best water footprinting method for you. Water footprints can give you valuable insights about the environmental impacts associated with water use in your product or process and can help support stakeholders and decision makers fight against global water scarcity. The field of water footprint is still developing, with new research and best practices continually being developed.
Please feel free to reach out to us if you have any questions or comments about water footprinting or how it could help your organisation.