Int J Life Cycle Assess (2014) 19:1336–1344

DOI 10.1007/s11367-014-0732-3

WATER USE IN LCA

The Water Impact Index: a simplified single-indicator approach

for water footprinting
Jean-Baptiste Bayart & Sébastien Worbe &
Julien Grimaud & Emanuelle Aoustin

Received: 21 December 2012 / Accepted: 12 March 2014 / Published online: 10 April 2014
# Springer-Verlag Berlin Heidelberg 2014

Abstract indicators related to water, from the ReCiPe life cycle impact
Purpose Along with climate change-related issues, improved assessment (LCIA) methodology.
water management is recognized as one of the major chal- Results and discussion Onsite water use is the main contribu-
lenges to sustainability. However, there are still no commonly tion to the Water Impact Index for both wastewater manage-
accepted methods for measuring sustainability of water uses, ment schemes. The release of better quality water is the main
resulting in a recent proliferation of water footprint method- driver in favour of the scenario including a wastewater treat-
ologies. The Water Impact Index presented in this paper aims ment plant, while the energy and chemicals consumed for the
to integrate the issues of volume, scarcity and quality into a treatment increase the indirect water footprint and carbon
single indicator to assess the reduction of available water for footprint. Results obtained with the three midpoint indicators
the environment induced by freshwater uses for human depict similar tendencies to the Water Impact Index.
activities. Conclusions This paper presents a simplified single-indicator
Methods The Water Impact Index follows life cycle thinking approach for water footprinting, integrating volume, scarcity
principles. For each unit process, a volumetric water balance is and quality issues, representing an initial step toward a better
performed; water flows crossing the boundaries between the understanding and assessment of the environmental impacts
techno-sphere and environment are multiplied by a water of human activities on water resources. The wastewater treat-
quality index and a water scarcity index. The methodology ment plant reduces the Water Impact Index of the wastewater
is illustrated on the current municipal wastewater management management system. These results are consistent with the
system of Milan (Italy). The Water Impact Index is combined profile of the three midpoint indicators related to water from
with carbon footprint to introduce multi-impact thinking to ReCiPe.
decision makers. The Water Impact Index is further compared
to results obtained using a set of three life cycle impact Keywords Life cycle impact assessment . Water footprint .
Water quality . Water scarcity . Water use

Responsible editor: Stephan Pfister

1 Introduction
Electronic supplementary material The online version of this article
(doi:10.1007/s11367-014-0732-3) contains supplementary material, Water is essential to sustain life and ecosystems. Yet, water
which is available to authorized users.
demand and pollution from human activities are continuously
J.<B. Bayart : S. Worbe (*) increasing (OECD 2012). Environmental issues pertaining to
Veolia Environnement Recherche et Innovation, Chemin de la Digue,
water are recognized as one of the major environmental con-
78603 Maisons-Laffitte, France
e-mail: sebastien.worbe@veolia.com cerns for the coming decades (UNESCO 2006).
Life cycle assessment (LCA) currently addresses water
J. Grimaud use-related impacts to some degree. The release of substances
Veolia Water North America, Indianapolis, IN, USA
in water bodies has been largely integrated in life cycle impact
E. Aoustin assessments (LCIA) through different impact categories. At
Veolia Environnement, Paris, Île-de-France, France the midpoint level, existing LCIA methodologies such as
Int J Life Cycle Assess (2014) 19:1336–1344 1337

ReCiPe (Goedkoop et al. 2009) or Impact 2002+ (Jolliet et al. The Water Impact Index takes into account both the quan-
2003) propose indicators for characterizing water ecotoxicity, tity and quality of water withdrawn and returned into the
eutrophication or acidification. At the damage level, water environment as well as the local scarcity of freshwater re-
pollution generally affects ecosystem quality and human sources. The main feature of the indicator is to remain as
health-related damage categories. simple as possible for the sake of clarity and transparency
The consideration of water as a natural resource and sub- for non-LCA experts, yet relying on life cycle thinking. This
sequent issues of freshwater scarcity and availability are metrics should then be able to give a preliminary assessment
inadequately addressed in LCIA methodologies (Koehler of the relative magnitude of potential impacts related to fresh-
2008) and have been the focus of several recent developments. water availability generated by a human activity.
Early in 2007, the UNEP SETAC Life Cycle Initiative
launched the Water Use in LCA (WULCA) working group 2.1.2 Scope of application
(Koehler and Aoustin 2008). One outcome was a framework
identifying cause-effect chains that should be addressed for The proposed Water Impact Index could serve a number of
considering impacts of off-stream freshwater use in LCA purposes, including but not limited to the following:
(Bayart et al. 2010). Characterization factors have also been
proposed by several authors. The second phase of the & Screening assessment of water use: identification of water
WULCA working group delivered a review of these existing hotspots in the value chain and of major improvement
methods (Kounina et al. 2013). More recently, a weighted leverage opportunities.
water footprint, integrating both consumptive and degradative & Decision support: The methodology may be used to sup-
water use, has been proposed by Ridoutt and Pfister (2013). port decision makers by providing a single indicator for
Berger and Finkbeiner (2013) also promoted several research impacts related to water availability.
pathways to improve water footprinting. & Communication: The Water Impact Index may be used for
These efforts have been important to assess comprehen- communication purposes, both for consumers and for
sively impacts of human activities on water resources and corporate reporting.
broadening the relevance of LCA to the broader scope of
environmental impacts being considered. These methodolo- However, using the Water Impact Index does not provide a
gies have also been questioned, particularly by non-LCA comprehensive assessment of water-related environmental
experts on grounds that the units of impact category indicators impacts. This initial screening approach should be followed
are inaccessible to a non-alert audience (Ernst and Young by a more detailed LCA study using a wider range of impact
2013). The French platform on eco-labelling also argues that categories.
the number of environmental indicators should be limited
(AFNOR 2011). These observations highlight the need for a 2.2 Calculating the Water Impact Index of a unit process
single indicator that incorporates and integrates multiple var-
iables to address water-related impacts. The purpose of this Figure 1 illustrates a unit process withdrawing water from
paper is to address these concerns by proposing a single different sources (W1; W2;…; Wi), and returning water to
indicator, the Water Impact Index, to address the water foot- different water bodies (R1’; R2’;…; Rj). The Water Impact
print associated with the environmental impacts of water use, Index of a unit process is calculated according to Eq. (1).
both in terms of quantity and quality.
X  Xh i
Water Impact Index ¼ i
W i ⋅Q W i
⋅WSI i − j
R j ⋅Q R j
⋅WSI j

2 Methods ð1Þ

2.1 The Water Impact Index: goal and scope

where:
2.1.1 Specification for this new metric
& Wi and Rj are quantities of water withdrawn from water
The Water Impact Index intends to assess in a simplified body “i” and returned to water body “j”, respectively (in
approach the water deprivation cause-effect chains, related volume unit).
to water use, as described in Bayart et al. (2010). The Water & QW i and QR j are quality indices of water withdrawn from
Impact Index expresses changes in freshwater availability and water body “i” and returned to water body “j”, respective-
quality generated by a human activity and evaluates how the ly (unitless).
environment would potentially be deprived of freshwater re- & WSIi and WSIj are water scarcity indices for water bodies
sources at a local scale. “i” and “j”, respectively (unitless).
1338 Int J Life Cycle Assess (2014) 19:1336–1344

Fig. 1 Water used by a unit process

In this multiplication, or geometric aggregation, each term consumptive use), is considered as a net loss of freshwater
is implicitly affected by an exponent of 1, meaning that an availability.
equal weight is considered for quantity, scarcity and quality of
water. The indicator is then proportionally affected by the 2.2.2 Quality index
variations of each parameter. This value choice implies that,
for instance, an increase of water consumption inducing a The volume of water is weighted by a quality index that
10 % decrease of returned water would have the same effect intends to express water quality into a single grade, scaled
on the result than a decrease of output water quality by 10 %. between 0 (worst quality) and 1 (best quality). For a specific
The Water Impact Index is expressed in volume unit water pollutant, the higher the concentration, the lower the specific
impact index equivalent. For instance, a result of a cubic metre quality index is. In other words, multiplying volume by qual-
equivalent corresponds to the lost availability of a cubic metre ity index means that withdrawing high-quality water results in
of good-quality water, in a region facing severe hydrological lower water availability for other users than withdrawing low-
stress (quality index and water scarcity index both equal to 1), quality water. Alternatively, the higher the quality of the water
or to the lost availability of 2 m3 of good-quality water, in a returned to the environment, the higher the increase in water
region facing moderate hydrological stress (quality index availability is, compared to returning water of low quality
equal to 1 and water scarcity index equal to 0.5). back into the environment.
This formula sets up a general framework for the Water QW i and QW j are calculated according to Eqs. (2) and (3):
Impact Index. The following paragraphs define explicit oper-  
ational options for calculating each term of the equation. This Cref p
QW i ¼ minimump 1; ð2Þ
framework is however not tied to these specific solutions, and C W i;p
it should evolve with the state of knowledge.

2.2.1 Consideration of water withdrawal and returned water  

Cref p
by the unit process QR j ¼ minimump 1; ð3Þ
C R j;p
A mass balance between water withdrawn from and returned
into the different water bodies is calculated. The water with-
drawn is accounted for with positive values (reduction of Where:
freshwater availability) whereas the water returned is
accounted for with negative values (increase of water avail- & Crefp (or reference concentration for pollutant p) corre-
ability), so the impact increases with the quantity of water sponds to the concentration of a specific pollutant p in
withdrawn and decreases with the quantity of water released. water that should not be exceeded in order to protect the
The net consumption of a process, generated by freshwater environment (in units of concentration). These reference
evaporation or integration into a product (so-called concentrations are also called “ambient water quality
Int J Life Cycle Assess (2014) 19:1336–1344 1339

standards” in order to distinguish them from drinking carbon footprint to introduce multi-impact thinking for deci-
water quality standards and effluent standards (Hoekstra sion makers. Historically, the majority of Milan’s sewage was
et al. 2011). A set of reference concentrations for pollutant sent to the Vettabbia stream without any treatment. Since
of main concerns in several countries can be found in the 2005, this water has been sent to the Nosedo Wastewater
Electronic supplementary material. Treatment Plant (WWTP), which has a capacity of 1.5 million
& CWi,p and CRj,p correspond to the effective concentration of person-equivalents. Two thirds of the treated water is returned
pollutant “p” in the water withdrawn from water body “i” to the Lambro River. The remaining portion is reused for
and returned into water body “j”, respectively. irrigation. Before Nosedo’s WWTP construction, farmers
used to withdraw water from the Vettabbia stream for their
The quality index is calculated according to the most irrigation needs.
penalizing pollutant. This “one out, all out” principle is used The functional unit includes the handling of Milan’s
in the Water Framework Directive for which the surface water wastewater (148.8 million m3/year) and irrigation water
status is determined by the poorer of its ecological status and supply (49.6 million m3/year) over a year. The current
its chemical status (Directive 2000/60/EC 2000). The widest wastewater management system (WWTP+reuse scenario)
spectrum of pollutants suspected to be found in the water is compared with the previous scenario without WWTP
should be investigated, and typical pollutants of some activi- (no WWTP scenario) (Fig. 2). For the no WWTP scenario,
ties should be studied carefully (i.e. pesticides and nutrients system boundaries include wastewater discharge into the
for agriculture, chemical oxygen demand (COD) for the food river, withdrawal of water for irrigation (foreground pro-
and beverage industry, etc.). Consolidating several pollutants cesses) and the energy needed for wastewater collection
into a composite quality index is further discussed (Section 4). (background processes). For the WWTP+reuse scenario,
The Electronic supplementary material provides the most the treated water discharged into the Lambro River is
stringent water quality standards for surface freshwater within considered (foreground process), as well as energy and
various countries, for a set of pollutants covering different chemicals required for wastewater collection and treatment
environmental issues. Quality standards can differ across (background processes). The treated water used for irriga-
countries according to several reasons (specificities of local tion is considered as an intermediate flow and is therefore
ecosystems, environmental background concentrations or re- not considered for this scenario. Infrastructure and raw
strictiveness of the legislation). The influence of these varia- water withdrawal for drinking water production are exclud-
tions on the results should be cautiously assessed especially in ed from system boundaries. The energy consumed by
a study implying inputs from various countries. In a first pumps for irrigation remains the same in the two scenarios;
iteration, the same ambient water quality standards could be it is then excluded from system boundaries.
used to characterize both direct and indirect water uses, and Primary data, based on average exploitation for the year
then specific quality guidelines of the supply chain’s countries 2009, have been collected from the operators for calculating
could be applied for a more detailed assessment. the Water Impact Index of foreground processes (or direct
Water Impact Index). These data include volumes of water
2.2.3 Water scarcity index withdrawn from the environment and returned into the envi-
ronment (Table 1), as well as several quality parameters
The water scarcity index addresses the potential local physical (COD, BOD, nitrogen, total phosphorous, total suspended
lack of water in a given area. Following current recommended solids, ammonia and six metals) to compute quality indexes
practices (Ridoutt and Pfister 2013) and as it presents a global (Table 2). The exact location of the plant has also been used
coverage, the Water Stress Index proposed by Pfister et al. for estimating the WSI as set by Pfister et al. (2009).
(2009) is used. This index is readily available and ranges from Evaporated water over the wastewater treatment plant has
0.01 (no scarcity) to 1.0 (high scarcity), and it is calculated as a been estimated based on open water surfaces of the plant and
function of the water withdrawal-to-availability ratio, the var- average evaporation data from the European Watch project
iability of freshwater availability and the storage capacity of (Harding and Warnaars 2011).
the study area. Further improvements and updates of the stress Chemicals and energy consumed by the plant are used to
index can be expected and should be adopted. calculate carbon footprint with the EcoInvent database (Swiss
Centre for Life Cycle Inventories 2009) and 100-year tempo-
2.3 Illustrative example ral horizon, and global warming potentials (Solomon et al.
(2007)). The Water Impact Index of background processes
An illustrative case study on the wastewater management (i.e. indirect Water Impact Index) is calculated, thanks to the
system in Milan (Italy) is presented in order to illustrate the Water Database (Quantis 2011). Due to a lack of information
operability of the methodology and its usefulness as a decision on background process, two basic assumptions are made and
support tool. The Water Impact Index is combined with a will be then briefly discussed:
1340 Int J Life Cycle Assess (2014) 19:1336–1344

Fig. 2 Compared scenarios. Above, without wastewater treatment plant (no WWTP). Below, with wastewater treatment plant and reuse by farmers
(WWTP and reuse)

& The quality of water withdrawn from the environment is 3 Results

assumed to be high (QW =1).
& Without precise information on the exact water use loca- 3.1 Using the Water Impact Index as a decision support tool,
tion of unit processes, average country-based WSI values complementary to carbon footprint
have been used (Average WSI in Italy of 0.27 and average
WSI in France of 0.18). For both scenarios, direct water use is the main contribu-
tor to the indicators, both from a volumetric approach
Results obtained with the Water Impact Index are then (Table 1) and the Water Impact Index calculation
confronted to three water-related midpoint indicators from (Table 3). Small variations can be observed on the direct
the ReCiPe LCIA methodology, namely freshwater eutrophi- water balance between the two scenarios, due to evapo-
cation, freshwater ecotoxicity and water depletion (Goedkoop rated water over the wastewater treatment plant and water
et al. 2009). incorporated in the sludge.

Table 1 Water balance of the

studied scenarios (in m3/year) No WWTP WWTP+reuse

Direct water uses Returned water −148,870,680 −99,190,453

Water withdrawal 49,595,227 0
Freshwater consumed for Energy 268 89,320
background processes Chemicals 0 367,849
Total −99,190,185 −98,733,283
Int J Life Cycle Assess (2014) 19:1336–1344 1341

Table 2 Quality indexes of direct water uses (unitless) Table 4 Carbon footprint of Milan’s wastewater management system—
comparison of scenarios no WWTP and WWTP+reuse (in tons CO2
No WWTP WWTP+reuse equivalent/year)

Returned water 5.5×10−3 5.5×10−2 No WWTP WWTP+reuse

Water withdrawal 2.0×10−2
Electricity 76 25,500
Chemicals 0 1,500
Total 9,482 28,663

Regarding the no WWTP scenario, the Water Impact Index

is mainly generated by river water withdrawal for irrigation.
Although the volume of wastewater discharged into the Finally, electricity and chemical consumption are responsible
Vettabbia stream is high (148.8 million m3/year), the associ- for the increase of the carbon footprint (Table 4).
ated negative Water Impact Index is small with −41 241 m3 From a decision maker's perspective with environmental
water impact index equivalent (a negative Water Impact Index concerns, taking into account only carbon footprint would
indicates an increase of water availability). This result is due to have not been in favour of the WWTP solution. The introduc-
the low quality of the water discharged, which has then a tion of a volumetric-based water footprint would have
limited effect on freshwater availability increase. As energy comforted this point of view, whereas the Water Impact Index
consumption for wastewater collection is very low (mainly moderates the conclusion by accounting for water quality
gravitational network), the indirect Water Impact Index is not issue and supports decision making with a more vivid picture
significant for this scenario. This result is also reflected into of environmental impacts related to both solutions. The ap-
the carbon footprint evaluation (Table 4). proach usefully introduces multi-impact thinking.
Regarding the WWTP+reuse scenario, the total volume of
water discharged into the Lambro River is lower (99.2
million m3/year). However, the quality of the water discharged 3.2 Comparison with conventional LCIA methodology
into the environment is improved. The quality index increases
by a factor of 10 reflecting the effluent quality improvement The Water Impact Index methodology proposed here is a
provided by the WWTP. On the other hand, energy and simplified water footprint approach, and results must be con-
chemical consumption for wastewater treatment increase the sistent with those obtained using a more traditional LCIA
indirect Water Impact Index, which represents 11 % of the approach. Results obtained with the three water-related mid-
direct Water Impact Index benefit obtained through the dis- point indicators from the ReCiPe LCIA methodology depict
charge of treated water. This significant contribution can be similar tendencies than the Water Impact Index (Table 5). For
explained by the difference in Water Stress Index values the three impact categories, the additional indirect impacts
considered for direct and indirect Water Impact Index calcu- generated by energy and chemical consumption are compen-
lation (0.05 for Milan area, 0.27 on average for Italy where sated by a larger reduction of direct impacts.
electricity and part of chemicals are produced, and 0.18 on More specifically, the reduction of phosphorous and metals
average for France where the remaining part of chemicals is discharged in treated wastewater effluent returned to the en-
produced). However, the indirect water use for energy and vironment reduces, respectively, eutrophication and
chemical production still generates a lower additional Water ecotoxicity impacts. The reduction of water withdrawal for
Impact Index than the benefit obtained through improvement irrigation supply reduces the water depletion impacts. The
of water quality and reduction of raw water withdrawal. relative contribution of the processes is different as the impact

Table 3 Water Impact Index of Milan’s wastewater management system—comparison of scenarios no WWTP and wastewater treatment+reuse (in m3
equivalent/year)

No WWTP WWTP+reuse

Direct Water Impact Index Returned water −41,241 −277,733

Water withdrawal 49,992 0
Indirect Water Impact Index Energy 40 10,717
Chemicals 0 20,441
Total 8,791 −246,575

Negative numbers express an increase of water availability

1342 Int J Life Cycle Assess (2014) 19:1336–1344

Table 5 Water footprint profile of Milan’s wastewater management system—comparison of scenarios no WWTP and wastewater treatment+reuse

Freshwater eutrophication (kg P-eq/year) Freshwater ecotoxicity (kg 1,4-DB eq/year) Water depletion (m3/year)

No WWTP WWTP+reuse No WWTP WWTP+reuse No WWTP WWTP+reuse

Direct water use 5.06×105 8.93×104 8.78×105 5.86×105 4.96×107 0

Indirect water use 1.47×101 6.24×103 2.22×102 9.84×104 1.99×102 1.01×106
Total 5.06×105 9.55×104 8.78×105 1.57×105 4.96×107 1.01×106

category only accounts for water withdrawn, without consid- Abstracting water of higher quality increases the impact on
ering returned water or local scarcity issues. water resource, so the absolute result of the no WWTP sce-
From a decision support point of view, the conclusion nario is widely impacted by different input qualities. However,
obtained using the ReCiPe methodology and the Water Impact in this case study, a change in water quality does not invert the
Index is the same; the wastewater treatment plant reduces the conclusion between the two scenarios; the relative benefit of
overall water footprint of the wastewater management system. reusing water is only enhanced if it enables to avoid
abstracting water of higher quality.
3.3 Uncertainties and sensitivity analysis

Two main assumptions were made on the quality and the local 4 Discussion
scarcity for indirect water withdrawn, due to lack of specific
data on background processes. The methodology presented in this paper is pragmatic, focus-
The quality of indirect withdrawn water was assumed to be ing on its applicability for practitioners. Its main feature is to
high (Q=1); this conservative assumption equally affects the integrate volume, scarcity and quality into a single indicator
indirect contribution of both scenarios which could be targeting ecosystem quality. It is conceptually quite similar to
overestimated. However, it does not significantly affect the the midpoint indicator proposed by Boulay et al. (2011). Both
results as the indirect contribution to water footprint is low indices tackle, however, two distinct areas of protection, hu-
compared to the contribution of direct water uses. man health for Boulay et al. (2011) and ecosystem quality for
An average country WSI (0.27) has been selected for each the Water Impact Index. Indeed, Boulay et al. (2011) inte-
background process, assuming that electricity and chemical grates the quality of water by classifying water into different
production are equally spread over the Italian territory. The categories that are functional for specific human uses (drink-
uncertainty surrounding the aggregation of the WSI at country ing water, agriculture, industry, etc.), while the Water Impact
level is significantly high for Italy (Pfister and Hellweg 2011). Index aims at reflecting the quality of water regarding targets
However, as the background processes account for a small that should be met to ensure good ecological status of natural
contribution on the total result, result tendencies would remain water bodies. While designed to target two distinct issues, the
the same, even with the highest possible WSI for background two methods could implicitly overlap, and a quantitative
processes. comparison of their complementarities and differences would
The Water Impact Index depends on input water quality be the topic for further research.
(Qin); Table 6 shows the sensitivity of this parameter in the no As a simplified approach, the Water Impact Index obvious-
WWTP scenario, where water is withdrawn from the river. ly presents some limitations and cannot replace a

Table 6 Sensitivity of the Water Impact Index in the no WWTP scenario (in m3 equivalent/year) regarding withdrawn water quality

No WWTP Poorer water Higher water

quality abstracted quality abstracted

Water quality of withdrawn water (Qin) 0.02 0.001 1

Direct Water Impact Index Returned water −41,241 −41,241 −41,241
Water withdrawal 49,992 2,500 2,499,600
Indirect Water Impact Index Energy 40 43 43
Chemicals 0 0 0
Total 8,791 −38,698 2,458,402
Int J Life Cycle Assess (2014) 19:1336–1344 1343

comprehensive water footprint. Further developments to en- combination of these two aspects is not achieved yet. Further-
hance the relevance and the robustness of the Water Impact more, there are large uncertainties associated with underlying
Index should be encouraged. data on groundwater recharge (Döll and Fiedler (2008)) and
The quality index is calculated according to the most the spatial resolution at large watershed level might be inad-
penalizing pollutant and is then affected by a so-called equate to properly assess monthly scarcity (Pfister and Bayer
masking effect on the variation of other pollutants. This (2013)), so the relevance of pursuing these aspects of refine-
approach still lacks consensus, as it cannot take into account ment still needs to be proven.
the addition of other pollutants into a water flow. If the
specific quality index associated with these additional pol-
lutants remains higher than the quality index calculated for
the most penalizing pollutant, then the Water Impact Index 5 Conclusions
does not capture the additional environmental impact. An-
other approach could be to avoid this masking effect by Improvements of LCA schemes regarding the integration of
combining the different pollutants into a single water quality environmental impacts generated by water use are required to
index. This aggregation could be done using characterization better measure and understand the pressure of human activi-
factors of LCIA methodologies; however, LCIA methodol- ties on water resources. In the meantime, the development of
ogies such as Impact 2002+ or CML 2011 do not provide a meaningful single indicators for water footprint is also needed
common unit for impact categories addressing water pollu- for decision makers.
tion (Guinée et al. 2001; Jolliet et al. 2003). What is more, This paper proposes a new metric, the Water Impact
the quality index relies on existing ambient water quality Index that simplifies water use assessments. It consists of
standards and is bound to the availability of such values. combining the volume of water used, the change in water
The quality index could therefore be overestimated if no quality and the local water scarcity into a composite
Cref is available for some pollutant, as impacts can be single indicator. This operational methodology is illustrat-
underestimated in traditional LCA when no characterization ed on a municipal wastewater management system to
factors are available for some substances. In addition, these demonstrate the possibility of using the Water Impact
standards might not always be defined with the same phi- Index as a simplified decision support tool for improving
losophy across different countries. water management of a product system. In this case,
Secondly, neither the size nor the background pollution of conclusions derived from Water Impact Index assessment
receiving water bodies is considered in the methodology results match those from a more traditional LCIA ap-
proposed and in any LCIA methodology. The flow rate of proach. However, a more extensive statistical validation
the receiving river does have an incidence on potential of the comparison between the Water Impact Index and
impacts of effluent discharges. Pollutants discharged would more traditional available LCA methodologies is also
be more or less diluted into water bodies. Similarly, it would warranted. The third project of the WULCA group is
be valuable to consider the pollutant background level in expected to address this issue with a quantitative compar-
order to distinguish the assimilation capacity among differ- ison of methodologies for assessing water use impacts in
ent receiving water bodies. While it seems feasible to inte- LCA.
grate these two concepts for calculating the Water Impact Water footprinting is still a new concept, and there is no
Index (but also life cycle assessment results) of foreground clear methodological consensus when compared, for instance,
processes, it would be more complex for background pro- to carbon footprint. It is also a gaining momentum, and the
cesses because of the lack of generic data for these param- need for research in this field has been highlighted. This paper
eters. These aspects could however be considered through is a building block that aims at expanding the range of avail-
local assessment such as risk assessment, and the two ap- able water footprint methodologies. Nevertheless, the best
proaches should be considered as complementary. methodology to be used often depends on the study’s goal
Further developments are also expected regarding the wa- and scope. Therefore, the main principles described in this
ter scarcity index. The distinction among different water re- paper could easily be used for designing customized water
sources and their interactions (i.e. groundwater, surface water) footprinting approaches.
would have a benefit in some prospective case studies. Defin-
ing seasonal water scarcity indices would also allow improv- Acknowledgments The authors wish to acknowledge the anonymous
ing the quality and the usefulness of Water Impact Index reviewers for their thoughtful comments and helpful suggestions. We are
assessments. Some water scarcity metrics already propose grateful for the support of (in alphabetical order) Sophie Barteau, Frank
Bénichou, Boris David, Daniel Dunet, Anne Flesch, David Houdusse,
these distinctions (see Boulay et al. (2011) for surface/
Oliver Keserue, Caroline Laget, David Lazarevic, Severine Mehier,
groundwater distinction and Hoekstra et al. (2012) or Pfister Massimiliano Naso, Ed Pinero, Pierre Ribaute, Ronald Richa and Gilles
and Bayer (2013) for monthly water scarcity). However, the Senellart for their inputs on this paper.
1344 Int J Life Cycle Assess (2014) 19:1336–1344

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