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Guest post by Dr Sarah McLaren, Associate Professor at Massey University and Director of the NZLCM Centre. This article originally appeared in the Summer 2011 (December) issue of IrrigationNZ News.

  • Have you heard that the water footprint of 1 kg beef is 15,500 litres, and of 1 kg cheese is 5,000 litres?

  • Did you know that Unilever has set itself a target of halving consumer use of water associated with its products by 2020?
  • Or that Walmart is in the process of asking all its 10,000 suppliers to provide information on total water use in their facilities, and their water use reduction targets?

These activities all reflect an increasing concern about the limited availability of freshwater for use in economic activities. Although there is plenty of water in the world, only 2.5% of it is freshwater — and most of this freshwater is stored as glaciers or deep groundwater. Therefore only a small proportion is available for use in human economic activities and by ecosystems. This freshwater becomes available to us via precipitation, and its collection in rivers and lakesa. The increasing demand for this water is a result of population growth, economic development, changes in lifestyles (mainly related to increasing demand for certain agricultural products), and climate changeb.

Much of the media coverage of this issue has focused on calculations of the virtual water content of different products. According to this approach, pioneered by the Water Footprint Network (WFN), volumetric water use at the different life cycle stages of a product is added together to give a total volumetric result for water used by a product. For example, the volumetric water use associated with a merino jumper would be the total of the water used for irrigation on a merino farm, washing and dyeing the wool, and washing by the consumer throughout the jumper’s lifetime (plus water use in associated activities such as electricity generation and fertiliser production).

However, there is a problem with this approach. Assessment of water use, and its environmental significance, is complicated by the fact that the significance of water use depends upon where water is extracted and used. Most people assume that the significance of using one litre water in central Africa is quite different from using one litre water in New Zealand — at least from an environmental perspective. But how can this difference be represented when comparing water use by alternative products and processes?

Water stress index for different regions of the world

Water stress index for different regions of the world c

This type of question has led to recent interest in water footprinting using a Life Cycle Assessment (LCA) framework. LCA is a technique for assessing the environmental impacts of products, processes and activities along their life cycles from extraction of raw materials, through processing, manufacture, distribution, use and on to final waste management. According to this approach, the environmental significance of water use may depend upon factors such as: water scarcity at the location where water is withdrawn from a water body; whether water is rainwater, surface water in a river or lake, or fossil water located in an underground aquifer; and whether water use ‘counts’ when the water is returned to the location of withdrawal within a short time period. Degradation of water due to pollution is also relevant. These types of issues are currently being addressed by the International Organisation for Standardisation (ISO) which has set up a Working Group to produce a standard (ISO 14046) on ‘Water Footprint: Requirements and Guidelines.’ Interested organisations in New Zealand are invited to become members of the International Review Group (IRG) that discusses and submits comments to this ISO Working Group; contact Sarah McLaren for more details.

Does any of this matter for New Zealand? The answer is yes for two main reasons: (1) we live in a globalised economy with a ‘virtual water trade’ of about 1000 km3/yeara, and so water shortages elsewhere in the world can potentially be compensated by water used in production processes in New Zealand where products are then exported, and (2) we can position our exported products for competitive advantage by measuring their water footprints, driving improvements, and demonstrating their water footprint credentials. The five partners in the New Zealand Life Cycle Management Centre (Massey University, AgResearch, Landcare Research, Plant and Food Research, and Scion Research) have all worked in this area and are able to assist with measuring and reducing the water footprints of our exported products.

References:
a Oki, T., & Kanae, S. (2006). Global hydrological cycles and world water resources. Science, 313, 1068-1071.
b UNESCO-WWAP (2009). The United Nations world water development report 3: Water in a changing world. Paris, France: The United Nations Educational, Scientific and Cultural Organization.
c Pfister, S., A. Koehler, & Hellweg, S. (2009). Assessing the environmental impacts of freshwater consumption in LCA. Environmental Science & Technology, 43(11), 4098-4104.