Sustainable Water | The concept of Water Footprint

“We shall not finally defeat AIDS, tuberculosis, malaria, or any of the other infectious diseases that plague the developing world until we have also won the battle for safe drinking-water, sanitation and basic health care.” 

Kofi Annan, former United Nations Secretary-General

We use everyday a lot of water for drinking, cooking and washing, but even more water is used to produce those things that we use, such as food, paper, cotton clothes, etc. The water footprint is an indicator of water use that looks at both direct and indirect water use of a consumer or producer. The water footprint of an individual, community or business is defined as the total volume of freshwater that is used to produce the goods and services consumed by the individual or community or produced by the business.

The water footprint concept

The concept was first introduced by Hoekstra in 2002, as of not only the direct water use of a consumer or producer, but also at the indirect water use. The water footprint can be regarded as a comprehensive indicator of freshwater resources appropriation. The water footprint of a product is the volume of freshwater used to produce the product, measured over the full supply chain. It is a multidimensional indicator, showing water consumption volumes by source and polluted volumes by type of pollution; all components of a total water footprint are specified geographically and temporally. In the development of a water footprint three types of water are assessed: green water, blue water and grey water.

Blue Water: the blue component refers to consumption of water resources [surface and ground water], whereby consumption refers to the volume of water that evapo- rates or is incorporated into a product. This is more easily thought of as the irrigation water that is not returned to either the surface or groundwater. For the production of a product this is defined as the amount of water withdrawn from groundwater and surface water that does not return to the system from which it came.

Green Water: the green component is the volume of rainwater consumed. This is therefore particularly relevant to agricultural products. The evaporative loss is included as a component part of the water footprint because a significant proportion of the water would be available to other water users [e.g. groundwater reserves, ecological features] if the crops were not grown.

Grey Water: the grey component refers to the volume of polluted water associated with the production of goods and services, quantified as the volume of water that is required to assimilate pollutants to such an extent that the quality of the ambient water remains above agreed water quality standards. China is the country with the largest grey WF within its borders: which is 26% of the global grey water.

The distinction between green and blue water is extremely important, particularly in crop production given the significant differences in the management of rain-fed agriculture and irrigated agriculture. It also highlights the various ‘opportunity costs’ of water use. Green and blue water are considered direct consumptive use while grey water is an indirect consumption. Each stage of a product creation could have two or three different components of green, blue or grey water.

The water footprint offers a wide perspective on how a consumer or producer relates to the use of freshwater in their systems. It is a volumetric measure of water consumption and pollution. It is not a measure of the impact on the local water environmental consumption and pollution. Water footprint gives a spatiotemporally information on how water is appropriated for various human purposes. It can therefore feed the discussion about sustainable and equitable water use and allocation and also form a good basis for a
local assessment of environmental, social and economic impacts. [I will have a post on the links between water footprint and carbon footprint]

Some facts and figures

  • The production of one kilogram of beef requires 15000 litres of water [93% green, 4% blue, 3% grey water footprint]. There is a huge variation around this global average. The precise footprint of a piece of beef depends on factors such as the type of production system and the composition and origin of the feed of the cow. [see report here]
  • The water footprint of a 150 gram soy burger produced in the Netherlands is about 160 litres of water. A beef burger from the same country costs about 1000 litres. [see report here]
  • The water footprint of Chinese consumption is about 1070 cubic meter per year per capita. About 10% of the Chinese water footprint falls outside China. [see report here]
  • Japan with a footprint of 1380 cubic meter per year per capita, has about 77% of its total water footprint outside the borders of the country. [see report here]
  • The water footprint of US citizens is 2840 cubic meter per year per capita. About 20% of this water footprint is external. The largest external water footprint of US consumption lies in the Yangtze river basin, China. [see report here]
  • The global water footprint in the period 1996-2005 was 9087 Gm3/yr (74% green, 11% blue, 15% grey). Agricultural production contributes 92% to this total footprint. [see report here]

References:

Ercin, A. E. and A. Y. Hoekstra (2012). Carbon and Water Footprints. Concepts, Methodologies and Policy Responses. United Nations World Water Assessment Programme, UNESCO. 4

Hoekstra, A. Y. and M. M. Mekonnen (2012). The water footprint of humanity. Proceedings of the National Academy of Sciences.

WWF (2011). Water Footprinting. Identifying and Addressing water risk in the value chain.

Chapagain, A. K. and S. Orr (2008). UK Water Footprint: The impact of UK’s food and fibre consumption on global water resources. Goldaming. UK, WWF-UK. 1.

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