The influence of methodology on the water footprint of
selected UK produced and consumed products
Rob Lillywhite1, Ashok Chapagain2, Tim Hess3
Background
•
Results - Potato
Water footprinting can be used to estimate both the
volume of water used to produce a product (virtual or
embedded water) and the environmental impact of that
water use
•
It is still an evolving discipline and various methodologies
and approaches are available depending on the
requirements of the study
•
The choice of methodology will influence the results and
interpretation, a situation which has resulted in
considerable variation in reported estimates on water use
and its impacts for different agricultural and food products
•
Stressweighted
Normalised
(H2Oe kg-1)
UK
107
10
17
Israel
147
103
171
•
Volumetrically, production in Israel uses one-and-a-half
times more water than the UK
•
But the stress-weighted and normalised approaches
suggest that the environmental impact may be ten-fold
Results - Strawberry
This Defra funded study prepared water footprints for
selected UK produced and consumed products: potato,
lamb, milk, strawberry, sugar and winter wheat
Methodologies
Volumetric
(litres kg-1)
Volumetric
(litres kg-1)
Stressweighted
Normalised
(H2Oe kg-1)
UK
176
12
20
Morocco
113
70
116
•
Volumetrically, production in Morocco actually uses onethird less water than the UK
•
However, the stress-weighted and normalised approaches
suggest that the difference in environmental impact may
be six-fold as Morocco is a severely water stressed country
Discussion
•
The volumetric water footprint developed by The Water
Footprint Network (Hoekstra et al., 2011). This approach
estimates the volume of green and blue (and grey) water
which is used/consumed during the different life cycle
stages of a product
•
The key to understanding and using these results is the
omission of green water from the stress-weighed and
normalised approaches. Green water use, principally
evapotranspiration, remains associated with the land
rather than the product
•
The stress-weighted water footprint (Ridoutt & Pfister,
2010). This approach estimates the volume of blue water
(as per the volumetric water footprint) and converts it to
an assessment of local water stress using a water stress
index (WSI) (Pfister at al., 2009)
•
The volumetric water footprint has been very successful in
raising awareness of the use of water and is invaluable for
water auditing purposes, but we conclude that it has
limited value for determining the local water stress of
globally sourced products
•
The normalised water footprint, H2Oe (Ridoutt et al.,
2012), is a development of the stress-weighted approach
in which the stress-weighted value is divided by the global
average WSI to give an assessment of water consumption
relative to a global average
•
A more balanced approach, especially within the LCA
framework, is possible using the normalised water
footprint alongside other environmental indicators, such
as eutrophication and acidification. This will provide a
more consistent and robust approach for environmental
and sustainability studies
Contact
1. University of Warwick, Wellesbourne, Warwick, UK
Email: robert.lillywhite@warwick.ac.uk
2. WWF-UK, Goldaming, UK
Email: AChapagain@wwf.org.uk
3. Cranfield University, Bedford, UK
Email: t.hess@cranfield.ac.uk
References
Hoekstra, A.Y., Chapagain, A.K., Aldaya, M.M., Mekonnen, M.M. (2011) The water footprint assessment
manual: Setting the global standard, Earthscan, London, UK.
Pfister ,S., Koehler, A., Hellweg, S. (2009) Assessing the environmental impacts of freshwater
consumption in LCA. Environmental Science and Technology 43 (11), 4098-4104.
Ridoutt, B.G., Pfister, S. 2010. A revised approach to water footprinting to make transparent the
impacts of consumption and production on global freshwater scarcity. Global Environmental Change
20, 113-120.
Ridoutt B,G., Sanguansri, P., Freer, M., Harper, G.S. (2012) Water footprint of livestock: comparison of
six geographically defined beef production systems. International Journal of LCA 17: 165-175.
Warwick Crop Centre
Rob Lillywhite
www.warwick.ac.uk/go/wcc