An update on water footprints

Since the coining of the term carbon footprint to refer to the sum of greenhouse gas emissions and removals, expressed in the units CO₂ equivalents, associated with a product, an organization or some other entity or activity, the term footprint has been applied to a wide range of environmental and even social measures. While it’s great to see such enthusiasm and innovation around sustainability assessment and reporting, there is also the potential for the term to create a lot of confusion, especially when it’s used in different ways. This can actually hinder adoption. For decision-makers in industry and government there are risks associated with applying a metric that can be calculated in numerous ways and produce, in some cases, results which are completely contradictory. For ordinary citizens, who lack technical awareness of the calculation methods, footprint claims can be meaningless or even misleading. This is particularly the case for water footprints, due to the complexity of water-related issues and the variety of approaches that have been taken to their assessment. The purpose of this blog is to summarize some important recent developments in water footprint standardization and application.

Why do we need water footprints?

Technical efficiency measures, like energy use efficiency and water use efficiency, are relevant in some circumstances, but not others. For example, water use efficiency can be used to compare different water using appliances such as washing machines and dishwashers (i.e. litres used per cycle). For products such as these, water use efficiency labelling for consumers is actually mandatory in some countries. In this situation, water use efficiency makes sense as a performance measure because the overwhelming majority of water use occurs in just one stage of the product’s life cycle – the use stage. Water use in the manufacturing, distribution and disposal of these appliances is usually trivial in comparison.

 Water use efficiency can also be used to benchmark the technical efficiency of factories or farm operations. In Australia, where farming is often practiced in situations of low and variable rainfall and where water is often a growth limiting factor, water use efficiency is a longstanding goal, closely linked to agricultural productivity. However, it is critically important to recognize that water use efficiency is a performance measure that fails to provide information about the situational context. Achieving high levels of water use efficiency is more important in, for example water stressed regions, than others. In some locations, especially where water resources are abundant, other environmental issues could be a much higher priority.

Footprint metrics are informative when a life cycle perspective is needed to adequately evaluate environmental performance. For many types of products, especially food and beverages, water use can occur at various life cycle stages (e.g. during the production of farming inputs like fertilizers and agricultural chemicals, during farming operations, during processing) and in a variety of geographical locations (e.g. since food ingredients may be sourced from different countries). For these types of products water use efficiency is not a relevant metric as it makes no sense to aggregate different types of water consumed in regions where different local environmental contexts exist.

It is in this situation that water footprints are important. Water footprints look beyond the quantity of water being used and involve an assessment of the potential environmental impacts associated with the water use in question. The inclusion of an impact assessment step makes it possible to compare products and systems where there is geographical and even temporal (e.g. seasonal) variation in water use. Water footprints also make it possible to assess water use across the life cycle of a product so that the specific instances of water use with the greatest potential to be causing environmental harm can be identified. This is possible because each instance of water use is assessed using locally applicable impact assessment parameters. In many ways, the water footprint is like the carbon footprint. Emissions of different greenhouse gases are not simply aggregated; they are first multiplied by the relevant global warming potential and then expressed in a common unit (i.e. CO₂ equivalents).

The advantage of technical efficiency measures, such an energy use efficiency and water use efficiency, is that they can usually be directly measured and independently verified. In contrast, footprint metrics are calculated using models which can differ in scope, complexity and model parameter settings. In the case of carbon footprints, a variety of protocols, based on life cycle assessment (LCA), now exist (e.g. ISO/TS 14067, PAS2050, GHG Protocol Product Standard) and generally the 100-year global warming potentials published by the IPCC are used. In the case of water footprints, standardization of methods and parameters is a more recent phenomenon.

The international standard (ISO 14046: 2014)

The International Organization for Standardization (ISO) is the world’s largest international standard setting body. It is independent and non-governmental, whose membership is made up of national standardization bodies (currently more than 160). Although its history dates back to 1926, it was officially founded in 1947 as one of the first organizations established by the United Nations Economic and Social Council. Through its members, ISO brings together experts to share knowledge and develop voluntary, consensus-based, market relevant international standards that support innovation and provide solutions to global challenges (www.iso.org). Well known examples include the ISO 9000 series concerning quality management systems and the ISO 14000 series concerning environmental management systems.

The international standard for water footprints (ISO 14046) was published in August 2014 after five years of international negotiation. The process involved leading science experts from over 40 countries as well as representatives from organizations such as the World Business Council for Sustainable Development, the International Dairy Federation, the International Aluminum Institute and World Steel. ISO 14046 is the only international standard for water footprint developed through an open, multiparty, international and consensual process. ISO publishes a range of different types of documents. International standards represent the highest possible level of international consensus on a subject.

Key elements of ISO 14046 can be summarized as follows:

• Scope: Principles, requirements and guidelines for the quantification of water footprints, preparation of third party reports and undertaking a critical review. ISO 14046 is not concerned with the communication of footprints, which is the subject of a new international standard in development (ISO 14026).
• Application can be to products, services, and organizations.
• Water use is considered in the broadest sense and includes both water consumption and water degradation (pollution).
• There is strict control over the allowable use of the term water footprint which is only to the result(s) obtained after impact assessment modelling. The term cannot be applied to a water inventory (e.g. litre per hectare, litre per kg, litre per hour) or the results of virtual water calculations.
• There are many types of environmental impacts related to water use. Water consumption can increase water scarcity. Chemical emissions to water might contribute to eutrophication or acidification or have other toxicity impacts. According to ISO 14046, the term water footprint can only be applied when all relevant impacts related to water use have been assessed and reported. When only a specific aspect of water use has been assessed, a qualifying term must be added to avoid misunderstanding. For example, the term water scarcity footprint can be used to describe the results of a study which only addresses the impacts of water consumption (i.e. not also water pollution).

Water footprints can be used to inform strategic action to reduce environmental impacts related to water use, taking a life cycle perspective. A water footprint can also be communicated to stakeholders (investors, employees, supply chain partners, customers, etc.), many of whom are increasingly interested to know about the impacts of water use associated with organizations and products. Performance tracking over time is another option. It is important to note that ISO 14046 specifically addresses the environmental aspects of water use. It can be used alongside other tools which evaluate economic and social aspects of water use.

Water footprints for strategic insight

Organizations can take responsibility for reducing the environmental impacts directly associated with their operations. However, many organizations are also taking a supply chain or life cycle approach. For businesses in the food industry this is particularly important because very often the major sources of environmental impact do not fall within the sphere of their direct operations but occur at the agricultural stage.

Water footprint studies start by mapping supply chains and creating an inventory of water use associated with each supply chain activity. As mentioned above, water use can include water consumption as well as chemical emissions which impact water quality. Thermal pollution, where water is discharged at elevated temperature affecting local aquatic ecosystems, is another possibility. Insofar as possible, this information needs to be compiled taking into account the type of water (e.g. surface water, groundwater, recycled water) that is used and the location where this occurs. Land use change and land management that impact the flow of precipitation to surface and groundwater should also be noted (e.g. conversions from forest to pasture or vice versa). It is usual to find that some of this information can be readily compiled while other data are more difficult to come by. Life cycle assessment databases can be a helpful source of generic information. An initial assessment of the data usually reveals the critical parts of the supply chain which warrant more careful examination and other parts where estimates are sufficient. The process is usually iterative. It is not practical to study every part of a life cycle in the same detail. LCA impact assessment models can then be applied to evaluate the relative importance of the different instances of water consumption and pollution at the various life cycle stages.

A water footprint study report can be a rich source of information which can help organizations to understand their water related risks and environmental impacts. The absolute values are usually not so important; rather it is the identification of so-called hotspots – e.g. stages in the supply chain or particular ingredients that contribute disproportionately to the overall result. It is not uncommon to apply multiple different models which seek to characterize the same environmental impact. If the models provide coherent results, this increases confidence in the overall findings. Where models diverge, the reasons can be explored and this too can provide further insight. Working within the LCA framework is most important since this enables the relative importance of a water footprint to be assessed in the context of other types of environmental impacts. For example, many organizations start their engagement with LCA when they perform a carbon footprint. This might be later followed by a water footprint. An obvious question that arises is how significant the water footprint is relative to the carbon footprint. LCA provides the suite of integrated models to allow this question to be answered quantitatively. It is then necessary for the organization to prioritize because management time and financial resources that can be directed toward environmental improvement are not unlimited. In addition, there will typically be trade-offs to consider - practical interventions to improve one environmental performance measure frequently lead to impacts in other dimensions. For example, water treatment, water recycling and reuse are energy intensive. Most forms of electricity production are also water intensive (e.g. thermal and nuclear power plants, dams for hydroelectricity production). One of the most effective ways of reducing enteric-methane emissions from livestock is to improve the quality of the diet, but at what cost in terms of irrigation water use and fertilizer emissions? These types of questions highlight the importance of LCA, with its comprehensive evaluation of environmental performance and trade-offs, rather than issue-specific footprints as the basis for major strategic action.

Water footprints for environmental claims

Footprints come to the fore when communicating environmental performance to non-technical stakeholders in society. Compared to LCA study reports, footprints are simplified and they specifically address environmental issues that people are aware of and concerned about. Carbon footprints address community concern about climate change and there are now many third-party operated programmes which facilitate reporting of the carbon footprints of products and organizations. Similar programmes, based on ISO 14046, are expected to emerge soon to support water footprint claims, beginning most likely with water scarcity footprints.

However, unlike the situation described above where water footprint studies are used to inform an organization’s internal decision-making, with water footprint claims the absolute values are most important. Consumer laws demand that environmental claims are able to be substantiated and are not misleading. In addition, footprint claims are intended to allow comparison between products and organizations. Consistency in methods is therefore most important. At the present time there are a variety of regionalized water stress indices which are being used to calculate water scarcity footprints. Depending on the index chosen, different absolute water scarcity footprint results are obtained. To support future water footprint claims, a major consensus building process is being undertaken by WULCA, a project group of the UNEP-SETAC Life Cycle Initiative (http://www.wulca-waterlca.org/). A new dataset of characterization factors for calculating water scarcity footprints is expected to be released in 2016. To achieve comparability between footprints, the use of Product Category Rule (PCR) documents, which define other critical modelling choices, is also important. In this regard, ISO/TS 14027 is another new document under development which is intended to improve the quality and uniformity of PCRs.

A comment on water footprints of livestock products

Livestock and livestock products have been of considerable interest to many FCRN members. There have also been some rather outrageous statements made about the water footprint of livestock products, including claims suggesting the water footprint of any animal product is larger than the water footprint of crop products with equivalent nutritional value (Mekonnen & Hoekstra. 2012. Ecosystems 15:401-415). These claims are based on virtual water studies which, although bearing the name water footprint, are not compliant with ISO 14046.

The first thing that needs to be stated is that agricultural production systems are highly diverse – so there are differences in how livestock rearing and crop production are practiced. In addition, the local environmental contexts where farming is practiced vary – such as variation in local water scarcity. Broad brush claims about the footprints of entire categories of agricultural or food products are rarely, if ever, truly representative or useful.

To take an example: in the Australian State of New South Wales, the water scarcity footprints of six geographically defined beef cattle production systems were found to vary from 3.3 to 221 L H₂Oe per kg live weight (cradle to farm gate). The unit H₂Oe is analogous to the CO₂e used in the reporting of carbon footprints, except that the unit of equivalence is water consumption at the global average water stress index (based on http://www.ifu.ethz.ch/ESD/downloads/EI99plus). The main message is that the variation in water footprints is large, even within just one part of eastern Australia.

In another study, the water scarcity footprint of lamb cuts produced in western Victoria (Australia) and exported to the USA for consumption was 44 L H₂Oe per kg (cradle to grave). The water scarcity footprint of milk produced in Victoria’s South Gippsland region was 1.9 L H₂Oe per L (cradle to farm gate). For wheat produced in New South Wales, where there is very limited use of supplementary irrigation, the water scarcity footprint ranged from 0.9 to 152 L H₂Oe per kg grain (cradle to farm gate). Although there is no basis to make a direct comparison, as beef cattle and wheat have different pathways of transformation into food products which are eaten and they contribute to diets in different ways, the ranges in farm gate water footprints for beef cattle and wheat in New South Wales were largely overlapping. If anything, these results should evoke caution in making simplistic characterizations of the water footprints of different types of foods and diets.

Further information about footprint metrics

Ridoutt B, Fantke P, Pfister S, Bare J, Boulay AM, Cherubini F, Frischknecht R, Hauschild M, Hellweg S, Henderson A, Jolliet O, Levasseur A, Margni M, McKone T, Michelsen O, Milà i Canals L, Page G, Pant R, Raugei M, Sala S, Saouter E, Verones F, Wiedmann T. 2015. Making sense of the minefield of footprint indicators. Environmental Science & Technology 49(5):2601-2603.

Ridoutt B, Pfister S, Manzardo A, Bare J, Boulay AM, Cherubini F, Fantke P, Frischknecht R, Hauschild M, Henderson A, Jolliet O, Levasseur A, Margni M, McKone T, Michelsen O, Milà i Canals L, Page G, Pant R, Raugei M, Sala S, Verones F. 2016. Area of Concern: A new paradigm in life cycle assessment for the development of footprint metrics. International Journal of Life Cycle Assessment 21(2):276-280.

Further information about the WULCA initiative

Boulay AM, Bare J, De Camillis C, Doll P, Gassert F, Gerten D, Humbert S, Inaba A, Itsubo N, Lemoine Y, Margni M, Motoshita M, Nunez M, Pastor AV, Ridoutt B, Schencker U, Shirakawa N, Vionnet S, Worbe S, Yoshikawa S, Pfister S. 2015. Consensus building on the development of a stress-based indicator for LCA-based impact assessment of water consumption: outcome of the expert workshops. International Journal of Life Cycle Assessment 20:577-583.

Further information about ISO 14046

ISO 14046 (2014) Environmental management – Water footprint – Principles, requirements and guidelines. International Organization for Standardization, Geneva.

Further information about livestock water footprints

Ridoutt BG, Page G, Opie K, Huang J, Bellotti B. 2014. Carbon, water and land-use footprints of beef cattle production in southern Australia. Journal of Cleaner Production 73:24-30.

Ridoutt BG, Sanguansri P, Freer M, Harper GS. 2012. Water footprint of livestock: comparison of six geographically defined beef production systems. International Journal of Life Cycle Assessment 17:165-175.

Ridoutt BG, Sanguansri P, Nolan M and Marks N. 2012. Meat consumption and water scarcity: Beware of generalizations. Journal of Cleaner Production 28:127-133.

Ridoutt BG, Huang J 2012. Environmental relevance - the key to understanding water footprints. Proceedings of the National Academy of Sciences USA 109 (22): E1424.

Ridoutt BG, Williams R, Baud S, Fraval S, Marks N. 2010. The water footprint of dairy products: case study involving skim milk powder. Journal of Dairy Science 93:5114-5117.

Terminology

Water inventory: A compilation of water inputs and outputs related to a product, process, organization or activity. This should also include information about the resource type and location. For completeness a water inventory should also include quantification of chemical or thermal emissions which impact water quality.

Water footprint: ISO 14046 defines a water footprint as a metric or metrics that quantify the potential environmental impacts related to water use. These metrics are the results obtained when impact assessment models are applied to water inventory data. There can be several metrics, each reporting on a different type of impact (water scarcity, eutrophication, toxicity, etc.). As an option, LCA also provides techniques for aggregating impact category indicator results into a single score. Some studies address only specific aspects of water use, such as the impact of water consumption on water scarcity. Such studies of limited scope must be differentiated by a qualifying term (e.g. water scarcity footprint). To illustrate, a water scarcity footprint is usually calculated by first multiplying each instance of consumptive water use by a local water scarcity index. Only after application of the water scarcity index are the components of the water scarcity footprint aggregated into an overall result for the product. It makes no sense to simply aggregate a water inventory in a location of high water scarcity with a water inventory from a location of water abundance – the result becomes uninterpretable. The inclusion of an impact assessment step makes it possible to compare products and systems where there is spatial and temporal variation in water use.

Virtual water, embedded water: These terms generally refer to the total volume of water required to produce goods and services. The concept of virtual water, introduced by Professor Tony Allan of King’s College London, has been widely influential in raising awareness about the large quantities of water consumed in the production of everyday goods and services, especially food. Allan used the concept initially in the context of understanding trade and political affairs in the Middle East and North Africa. That said, these concepts are not appropriate for reporting or comparing environmental performance as the resource type and local environmental context are not considered. A rain-fed crop with a large virtual water content may be of less environmental concern than a crop with smaller virtual water content related to irrigation from a stressed aquifer. A case study illustration is presented in Global Environmental Change 20:113-120.

Blue water, green water: ISO 14046 does not refer to different colors of water. However, the terms blue and green water, originally introduced by Professor Malin Falkenmark, are sometimes conveniently used to differentiate water contained in water bodies (blue water) from water contained in the soil layers accessible to plant roots (green water). Sometimes the terms are also used to differentiate water abstracted from surface and groundwater from water supplied directly by precipitation.

Grey water: The water industry uses this term to refer to wastewater from households that lacks fecal or urine contamination (then referred to as black water). Less commonly, the term is used as a proxy water quality metric, being a theoretical volume of freshwater required to dilute a pollutant to a concentration level deemed acceptable. A range of more advanced methods that take into account the individual fate and effect characteristics of emissions are generally employed in LCA.

Water scarcity and water stress: These terms are defined in various ways and are sometimes used synonymously. In ISO 14046, water scarcity refers to the extent to which demand for water compares to the replenishment of water in an area. Water availability refers to the extent to which humans and ecosystems have sufficient water for their needs. Water availability therefore includes a water quality dimension.

Water footprints vs LCA

One of the principles of LCA is comprehensiveness (ISO 14040; 4.1.7), meaning that insofar as possible an LCA study considers all relevant exchanges with the environment related to resource use and emissions. The intent is to avoid problem shifting from one type of environmental impact to another. A water footprint study therefore differs from an LCA study in its scope – by addressing only environmental impacts related to water use. When only particular aspects of water use are studied, the term water footprint must be augmented with a suitable qualifying term (e.g. water scarcity footprint).