Purpose
This Policy Position Statement reviews the use of water
footprinting - and the linked concepts of "embedded water" and
"virtual water" - and sets out the position of the Chartered
Institution of Water and Environment Management (CIWEM) on the use
of water footprints.
CIWEM's position on water footprinting:
CIWEM welcomes the way that water footprinting
has drawn attention to the substantial volumes of water involved in
the production of food and other goods; but
CIWEM warns that volumetric water footprints
are only part of the information revealed by the process of water
footprinting, and that taken alone, water footprints do not measure
environmental damage. It all depends on the type of water
being used, what others uses it may be put to, with what benefits,
and where and in what state it is returned to the
environment. Considerable care needs to be taken in
using, comparing and interpreting published estimates of water
footprints.
The Chartered Institution of Water and Environmental
Management (CIWEM) is the leading professional body for the people
who plan, protect and care for the environment and its resources,
providing educational opportunities, independent information to the
public and advice to government. Members in 98 countries include
scientists, engineers, ecologists and students.
The issue in a nutshell
A water footprint is an estimate of the volume of fresh water
associated with the production of an item, or in the delivery of a
service.
Whilst the whole process of "water footprinting" can reveal when
and where water is used, and with what consequences, the volumetric
footprint itself cannot and does not convey such richness of
information, and is the poorer for it, if considered alone.
At first sight, the greater the volume of water appropriated for
use, the greater would seem to be the drain on resources and the
potential for adverse impact. But the impact of water use is
highly situational. It varies according to the source and
type of water being used, as between 'green', 'blue' and 'grey'
water.
[1] And whichever of these types is involved, the use of a
given (net) volume of water can have very different impacts at one
place compared to another, and at one time compared to another,
according to the availability of water, and the competing demands
upon it. In many cases, the non-return of water to the same
water body in the same quality causes net adverse impacts.
But in certain cases, water can be returned somewhere / sometime
else with a net positive impact - such as in the case of winter
abstraction and storage for summer irrigation purposes - so a large
water footprint is not necessarily a bad thing.
Background
A water footprint is an estimate of the volume of fresh water
associated with the production of an item, or in the delivery of a
service, throughout the full supply chain. It is typically
expressed as a volume of water per item, or per unit of production
(m3/kg), or per individual (m3/person).
The footprint includes all of the water associated with the
production of the goods or service, throughout the full supply
chain, whether directly in the process or indirectly to provide the
equipment, materials or transport needed. The footprint includes
all of the surface water and groundwater used, and (as appropriate)
the water transpired or evaporated from any crop or surface
involved in the production process. Any extra water that has to be
left in a river to dilute pollutants caused by the product/process
is also included (but this practice raises issues of local
standards and the risk of double counting). Water returned to
the source after use, at the same quality, is deducted from the
total volume, provided the point of return is not too far from the
point of abstraction. In that sense, the footprint is a measure of
net usage.
Water footprints determined in this 'all things included' way
can be surprisingly large. 140 litres of water (on average)
are said to be needed to produce one cup of coffee, and it is
estimated that 17,000 litres of water are needed to produce 1kg of
beef (EBLEX, 2010). A typical UK adult's diet is said
to have a water footprint of around 3,400 litres/day, compared to a
direct drinking water requirement of 10 litres/day and an overall
direct use (for domestic drinking, cooking, washing, watering and
sanitation purposes) of around 150 litres/day.
The terms "water footprint", "embedded water" and "virtual
water" are often used inter-changeably. Embedded water and
virtual water are both numerically and conceptually identical,
being the forerunner and final terms developed by Allen (1993,
1996) to define the water associated with the production of a good
or service. In contra-distinction, the process of water
footprinting was proposed by Hoekstra and Hung (2002) as a means of
estimating the impact on water resources of water appropriated in
the production of a good or service. But whilst the process
of water footprinting is broader in scope and intent to the concept
of virtual water, the numerical value of a water footprint is
derived in the same way as that of embedded and virtual water, and
all three measures are numerically identical. In
practice, those looking at global or regional trade in goods and
commodities have tended to use the term "virtual water", whereas
those interested in impact tend to use the term "water
footprint".
Benefits and warnings
Highlighting the size of
water footprints has been extremely beneficial in focusing public
attention on the volume of water required to produce food and goods
at source and to deliver them to end users. The huge
disparity between the local water resources used for personal needs
by an average individual in the developed world and that same
individual's all-in personal water footprint has been particularly
useful in drawing attention to hitherto overlooked
issues. A number of environmental organisations
campaigning for reduced water consumption have successfully used
these data to highlight the problems of water stress around the
world, and to encourage water saving at home and abroad. Some
businesses have used water footprints to identify supply chain
risks.
However, care must be taken not to use the concept too
simplistically. A water footprint is not a direct
measure of environmental impact. The timing and location of
the associated resources are vitally important aspects; the use of
a given volume of natural water resources has a different impact at
one place compared to another, and at one time compared to
another. For example, using water will have a much greater
environmental cost in a water-short catchment than in a water-rich
one, and be more much harmful during a dry season than during a wet
season. The impact of water resources use on society and the
environment is unlike the impact of carbon use and emissions in
this respect, because whilst carbon emissions impact globally,
through thorough atmospheric mixing, water resource use impacts
(like the depletion of an aquifer) are confined to a local area or
region, even when knock-on consequences are taken into
account. And even then, the impacts of land uses with high
absolute demands on local water resources need to be considered in
context and against the water demands of alternative land
uses. The following example illustrates the issue. If
meat is produced using irrigated grain grown in arid countries, it
is highly likely that major local water stress will result.
Here, an activity with a high water footprint is associated with a
high adverse impact. But sheep grazing on rain-swept
hillsides might have a similarly high water footprint, but very
little impact. Removing the sheep would not "save" water, or reduce
undesirable impacts.
Selecting between goods (or services) solely on the basis of the
volumes of water involved in their production can therefore be very
misleading.
As it stands, the numerical value of a water footprint alone is
not a measure of impact - it is just the virtual water summed over
the production line of a particular product or service.
Ancillary information on when, where and how water is used, and its
type, is also needed to judge the impact of water use. Some
organisations would prefer a definition of water footprint that
reflects the net environmental impact of the water use, rather than
the associated volume. This would avoid the problems above, and
provide a far better indicator, though it would be difficult to
produce in a consistent manner, because of the complex interplay
between relevant factors.
September 2011
Further information
For further information, see the FAQs page on the Water
Footprint Network's website at:
http://www.waterfootprint.org/?page=files/FAQ_Technical_questions
Note: CIWEM Policy Position Statements (PPS) represent the
Institution's views on issues at a particular point in time. It is
accepted that situations change as research provides new evidence.
It should be understood, therefore, that CIWEM PPS's are under
constant review, and that previously-held views may alter and lead
to revised PPS's.
[1] Some practitioners advocate the distinction between green,
blue and grey water.. The Water Footprint Network (see link
at the end) defines green water as that which condenses from the
'evaporative' flow (rainfall), blue water as that taken from
surface and groundwater sources (from the 'runoff' flow); grey
water as that which has been used (polluted) and returned (treated
or otherwise) to the runoff flow.
