See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/352749718 Circular economy of water: Tackling quantity, quality and footprint of water Article in Environmental Development · June 2021 DOI: 10.1016/j.envdev.2021.100651 CITATIONS READS 36 308 4 authors: Sébastien Sauvé Sébastien Lamontagne Université de Montréal The Commonwealth Scientific and Industrial Research Organisation 362 PUBLICATIONS 18,788 CITATIONS 105 PUBLICATIONS 2,513 CITATIONS SEE PROFILE SEE PROFILE Jérôme Dupras Walter R Stahel Université du Québec en Outaouais University of Surrey 87 PUBLICATIONS 1,602 CITATIONS 104 PUBLICATIONS 4,650 CITATIONS SEE PROFILE All content following this page was uploaded by Walter R Stahel on 02 September 2021. The user has requested enhancement of the downloaded file. SEE PROFILE Environmental Development 39 (2021) 100651 Contents lists available at ScienceDirect Environmental Development journal homepage: www.elsevier.com/locate/envdev Circular economy of water: Tackling quantity, quality and footprint of water Sébastien Sauvé a, *, Sébastien Lamontagne b, Jérôme Dupras c, Walter Stahel d a Department of Chemistry, Université de Montréal, Montréal, QC, Canada CSIRO Land and Water, Adelaide, SA, Australia Institut des Sciences de la forêt tempérée, Université du Québec en Outaouais, Ripon, QC, Canada d Product-Life Institute, Geneva, Switzerland b c A R T I C L E I N F O A B S T R A C T Keywords: Circular economy Water footprint Ecosystem services Sustainable water Water consumption The evaluation of the water footprint of goods is a good step towards the evaluation of the circularity of water. The assessment of the whole life cycle of a product allows the quantification of its actual consumption of water – including direct and indirect water usage as well as water devalued through contamination. The circular economy seeks to use resources within loops that allow their conservation. The water footprint allocation can be subdivided into blue (groundwater and surface water), green (rain water) and grey (contaminated water) but it must also integrate the circularity of the water to differentiate consumption that is in closed or closable loops from that which is open-ended. For example, rainwater harvesting should be renewable as long as harvest does not materially impact runoff from catchments or recharge rates to aquifers. Surface and groundwater consumption are acceptable if the minimal environmental water requirements of associated water-dependent ecosystems are met. Environmental water requirements are unique to different settings and include maintaining a suitable availability of water of sufficient quality downstream. In a changing world, the type of ecosystems that the society wants to maintain, build or reconstruct sets the stage for defining the appropriate environmental water requirements. In that respect, zero-impact groundwater use is especially difficult to achieve – sustainability here means how much impact from the exploitation of water, society is willing to tolerate in the longer-term. Investing in water increases its value to society. The water footprint estimations must be adjusted to better integrate circular economy concepts and lessen the focus on quanti­ fication of water consumption – it is not so much the throughput that matters but where does the water come from, what happens to it after use and how circular and sustainable it is. 1. Introduction Fresh water is precious, and it is probably the only resource for which we have no alternative. We are interested in the circular economy of water and in estimating the water footprint of diverse goods and activities to estimate their greenness and to what extent they are indeed sustainable. The circular economy seeks to conserve material goods within closed loops and thus prevent or at least minimize the linear process of resource extraction, transformation and disposal. This linear economy consumption is thus wasting * Corresponding author. E-mail addresses: [email protected] (S. Sauvé), [email protected] (S. Lamontagne), [email protected] (J. Dupras), [email protected] (W. Stahel). https://doi.org/10.1016/j.envdev.2021.100651 Received 7 June 2019; Received in revised form 21 May 2021; Accepted 6 June 2021 Available online 24 June 2021 2211-4645/© 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Environmental Development 39 (2021) 100651 S. Sauvé et al. material resources, energy and may also contaminate the environment. The concept of circular economy has evolved over the years, early named service economy (Stahel, 1997), or performance economy (Stahel, 2010), and its definition is intermingled with that of sustainable development (Sauvé et al., 2016). The definitions for circular economy have been thoroughly reviewed by Kirchher et al. (Kirchherr et al., 2017), and the business model implications are reviewed by Lüdeke-Freund et al. (Lüdeke-Freund et al., 2019). For our purpose, we will emphasize that the circular economy has always been about maintaining the value of stocks, be it natural, human, cultural, financial or manufactured capital, in a long term perspective (Stahel, 2019). It has evolved through three distinct phases, which today co-exist in parallel: a bioeconomy of natural materials ruled by Nature’s circularity, an anthropogenic phase characterized by synthetic (man-made) materials and objects, and a phase of ‘invisible’ embodied resources and immaterial constraints, such as producer liability. Applied to water – this also emphasizes that we are dealing both with the quantity and the quality of water. There are many alternate definitions for the circular economy and we purposefully want to avoid limiting the scope of the circular economy to material issues and manufactured objects and we seek to integrate concepts such as job creation, reindustrialisation of regions, extended producer liability and overall we focus on the sustainability of a mature circular economy which includes immaterial values (Stahel, 2016). Much of the circular economy literature deals with manufactured goods, its applications to the more elusive concept of water needs to be adjusted. For example, nearly 10 tons of water are consumed in the irrigation of the cotton used to produce a pair of jeans, with further contamination of process water to transform and dye the fabric (Leahy, 2014). If we insure a fully closed loop in our economic and resource consumption systems, we would include contamination issues and buffers to safeguard a healthier and safer environment for humans and wildlife. One possible illustration is that if we were to divert exhaust fumes inside our cars instead of to the envi­ ronment, we would be much more vigilant on the quantity and quality of that exhaust! Current economic assessments of resource consumption seldom include a full account of the generated externalities (like pollution). Albeit the biogeochemical cycle of water suggests an infinite loop and seemingly easy circularity; clean water evaporates from the surface of the earth and then falls back down as rain. The quantitative application of the circular economy concepts to water is somewhat more complex. Water in itself is indeed circular within a chaotic self-organized system, on the scale of the planet. The movements of water on a large scale reflect the water cycle of precipitation of rain, surface transport, evaporation and eventually return as rain. But on the local scale, there is a smaller water cycling where local water consumption and local “dispersal” of water actually contributes to evapotranspiration that will contribute humidity into the air and further local rainfall. Local land trans­ formation may have decreased soil permeability which would accelerate the evacuation of water, preventing infiltration and groundwater replenishment and aggravating soil erosion. In many ways, there are important questions of scale and the local envi­ ronment is critical when trying to tackle sustainability issues surrounding water (Krazcik et al., 2007). As others have emphasized, water cannot be conceptualized as a limited resource that is not being replenished but the limitations for renewal must be acknowledged (Biswas and Tortajada, 2019a). Water circularity as it occurs in the environment is no longer innocent as it can lead to contaminate the water in various ways. It can add nutrients, pesticides and pharmaceuticals to water as it transits through agricultural fields, it can provoke soil erosion, it will “wash” away contaminants from roads, it will heat water bodies trough usage in cooling and using water in various agri-food and industrial processes will release a plethora of contaminants into the environment. However, inherent but often unappreciated is the current extent of water reuse – in other words the water we consume is seldom ‘pristine’. During its transit from catchment back to a coastal city, water is used to flush excess nutrients from agricultural areas, dilute wastewaters are released from upstream localities or can be used for industrial purposes, such as for cooling power plants. Thus, what we need to do is to keep track of the water associated with what we do and what we consume. While water footprint estimations methods have been proposed and keep being improved, they do not yet fully encompass circular economy concepts, which are themselves elusive and in need of tighter definitions (Korhonen et al., 2018). Our objective is to illustrate some of the challenges associated with applying the concepts of the circular economy of water to the estimations of water footprint to better reflect impacts on the availability of water as a renewable resource. In and of itself, water is simply moving and changing state (as a liquid, vapor or ice). Concretely, we must really focus on water usage, where the water is coming from, where it ends and how its quality is changed along the way. Water itself cannot be defined as sustainable or not sustainable, it is our usage that defines its sustainability. To that purpose, we seek to find the best tools and means that should be implemented to track water usage along with the direct and indirect impacts. How should we assess the sustainable use of water? In particular, borrowing from the sustainable development concepts of safeguarding usage for later generations, circular economy integrates normative concepts to prevent pollution and indirect impacts that go beyond evaluations of water consumptions in liters. We must also emphasize that water has a dual personality with regards to sustainability. It definitely has a strong sustainability side in that when we need water to drink, for crops and many other uses – there is simply no alternative to drinking water (other potential liquids would all be water-based). But there is also a weak sustainability side to water in that efforts and human resources can be applied to improve the efficiency of its application or various wastewater treatment and reuse is also a form of weak sustainability where the same water can actually go a long way through many cycles of “consumption” and thus efforts increase the usefulness of a given volume of water. Despite all efforts towards reuse and optimized efficiency - we can increase and extend its usage in a weak sustainability understanding - but ultimately liters of waters are finite and drinking water is irreplaceable. 2. Objective This paper seeks to emphasize the various concepts used to tackle the concept of sustainability applied to water and how it relates to the circular economy thinking. We have sought the literature that intersects circular economy thinking and water. We specifically seek 2 Environmental Development 39 (2021) 100651 S. Sauvé et al. to explore some of the incongruent aspects of measuring water consumption and to advance the tools to measure virtual water, water footprint, and thus better define when water is sustainable and what is “circular water”. 2.1. Quantity vs quality of water Water is an omnipresent and indispensable resource; its circularity must be evaluated within a broad perspective that integrates the water-energy-food nexus and other issues associated with water. Thus, water usage must be evaluated both in terms of water quantity as well as water quality. This duality certainly complicates the evaluation of circularity, where liters of clean water must be compared to liters of contaminated water, the latter being a lost resource that the circular economy seeks to recuperate. Quantities of available water cannot be evaluated without looking at the quality of that water, we all need access to drinkable water (Biswas and Tortajada, 2019b). It is also an interesting case-study to compare the relative benefits of water usage for food vs energy production (W. Liu, Yang, Tang and Liu, 2019). There is also a significant energy and consumables consumption linked to production and transport of water. Water is inherently a “local” goods and that as a fluid, is it not easy to move around. For example, it is estimated that 20% of all electricity production in California is used to pump, treat, cleanse and deliver water (Glennon, 2009). For better or worse, water regulations are going to have a very local focus and each area is going to have to develop its own mechanisms to deal with the problem. This also highlights that local conditions could favor the retention of soil moisture, improving infiltration of rain that also reduces soil erosion, higher local evapotranspiration that can also help with more local showers, whereas other changes are negative: soil impermeabilization increases the transport of water out of the local system, reduce or eliminate groundwater replenishment, increases local temperatures (Krazcik et al., 2007). It is also noteworthy that natural systems such as forests are much better at providing local scale cycling of water than are intensive farms and land areas that have been managed and have had all marsh and wet areas that help to recharge groundwater removed and replaced with agricultural drainage and city sewers that quickly direct water out of the system and do no feed the small local water cycle. In water-limited areas, the focus must certainly be on water preservation, maximizing its use by minimizing losses and recuperating rainwater or water from any source. In arid, water-starved environments, water quantity is very sensitive and hence no efforts should be spared to enact all possible strategies to increase water use efficiency. Such environments are also at risk of worsening situations due to global warming (Novoa et al., 2019). Water quantity often controls water quality. For example, in the water-stressed Murray-Darling Basin of Southeastern Australia, reduction in river flows have been linked to an increased likelihood of blue-green algal blooms (Bowling et al., 2016). In regions where water is plentiful – the focus should rather be on water quality. Where there is a lot of water, it is very easy to get the impression that the water stream has a nearly infinite dilution capacity for contaminants. The main challenge in such environments is to ensure that water quality is preserved. In some temperate and northern environment, water scarcity is often not an issue, but water quality is affected by untreated or poorly treated wastewaters of domestic, industrial, or agri-food activities. In such environments, the main water challenge is not so much finding water, it is ensuring that the water for human usage is safe and that human activities do not contaminate surface waters. We also want to ensure that water does not cause adverse impacts on wildlife or reduce the potential ecosystem services that water would be providing such as recreational activities, fishing, wildlife habitat, spreading of chemical pollution or antibiotic resistance genes. We tend to overemphasize the need to recuperate water in water-rich environments. In such situations, the actual environmental impact of water consumption is dependent on the energy and consumables required for drinking water treatment and is akin to closing the lights when we leave a room. Many of the water shortages observed in such northern water-rich environments reflect the increased drinking water consumption to water lawns and the limited capacity of drinking water treatments plants – which is not the same as not having any water available in the river! When river flows are plentiful, excess water usage means too much water was pumped from the river and returned to it. In water rich areas, even the net export of contaminants is not affected by larger water consumption (the flux of contaminants in wastewater are simply diluted into more “wasted” water). The capacity to treat wastewaters could nevertheless be impacted and it could be more or less difficult to treat the more diluted wastewaters. A similar problem in water-stressed environments is assessing the relative environmental benefits of measures aiming to improve irrigation efficiency. An unintended benefit of poor irrigation practices is that some of the excess irrigation water returns to the environment (albeit possibly in a degraded state). Improved irrigation efficiency may not always return more water to the environment because some of the saved water is often used to irrigate more land instead (Government of South Australia, 2019). This issue is typical of conjunctive use of surface and groundwater, where quantifying the relative benefits of a management initiative can be difficult because measuring the exchange between groundwater and surface water in time and space remains challenging. 2.2. Indirect water usage The virtual water concept refers to the unseen water associated with a product, it is in itself somewhat elusive and hard to define (Allan, 2003). The virtual water and water footprint concepts have highlighted that we must consider water along the whole supply chain of what we consume. Thus, when looking at water preservation and the mass balance of water, we must not exclusively focus on direct consumption and must not forget indirect water usage. The consumption of water associated with a given product is usually not so much the water retained or held within the product itself but the water that was used to insure the production of this item (from agricultural irrigation for food, fibers or biofuels, process water for manufacturing or other indirect water consumption). This indirect water consumption is also evaluated through water footprint estimations and the means to assess and measure this have been well developed and keep being improved (Aldaya et al., 2011). Water used and not returned clean into a river would also be considered consumed. The challenges in such situations would be to both treat the water to remove the contaminants and prevent the resulting 3 Environmental Development 39 (2021) 100651 S. Sauvé et al. pollution of waterways, but also to recover those contaminants which are otherwise useful resources that should not be wasted (e.g. phosphorus is a fertilizer and a major contributor to algal blooms). In this case, water is both a resource in itself but also a vehicle to transfer other resources that become contaminants and that can pollute the environment if allowed to escape. To estimate the sustainability of water consumption, much efforts have been put towards evaluating the water footprint by further subdividing water appropriation into three groups: blue, green and grey (Hoekstra and Mekonnen, 2012). Blue water consumption can be defined as the volume of the water from either surface or ground water sources that was used to produce a given good, i.e., usually evaporated or integrated directly into the products. Green water consumption refers to the amount of rain water used. Grey water production is linked to contaminants in the water and reflects the volume of water required to dilute wastewaters to assimilate pollution and reduce contaminants below the appropriate quality thresholds. Estimating grey water is difficult as environmental quality regulations vary or may simply not be available for some target compounds. For example, when looking at most emerging contaminants, we know impacts are likely but thresholds have often not yet been established (Sauvé and Desrosiers, 2014) thus making the evaluation of the “grey” water very challenging for emerging contaminants. Another important difficulty in evaluating the blue/green consumption refers to liters of water that are actually consumed whereas grey water consumption refers to virtual liters of water that represent what would be needed to prevent excessive environmental impacts. Adding or comparing real and virtual liters of water may certainly become confusing if one attempts to estimate mass balance (Allan, 2003). Evaluation of grey water consumption must consider resource recovery; water becomes a vehicle for chemicals and materials that can be useful resources if recovered and put to good use (and thus prevent pollution and eutrophication in the case of nutrients such a phosphorus and nitrogen or the toxic impacts of metals). This illustrates that the evaluation of the environmental impacts of water consumption goes beyond the budgetary calculations of how much water is consumed and must integrate broader issues. It is important to estimate water whose quality has been diminished by its usage, it would seem more coherent to keep the calculation basis on the actual water consumption and not mix and match, consumed water with imaginary water that is needed to dilute the pollution (and dilution of pollution is a poor response to environmental problems). One important effect of considering indirect water consumption is to understand that it displaces water usage, i.e., even if we minimize direct water usage from domestic activities, consumption of those goods is connected to water consumed earlier from where those goods and services were produced. This water transfer often means that more northern, water-rich countries benefit from the indirect water consumption from more southern, water-poor countries – thus “importing” water and aggravating the water scarcity issues in places where water is most needed. Environmentally conscious consumers from water-rich regions of the world should therefore pay more attention to their indirect water consumption embodied in the goods they consume (e.g. cotton for jeans or coffee) than the direct water usage, which in relative terms, may have a much smaller environmental impact. This is comparable to envi­ ronmental footprint estimates for CO2 emission or energy consumption. The North-South exchanges of indirect water also raise ethical questions on the relatively cheap transfer of indirect water from often economically poor, water poor countries to their northern neighbours that usually have more resources (Chapagain et al., 2006). For example, a single cup of coffee is estimated to require 140 L of water for its production (Leafy 2014), and it is often produced in an area of the world that is more water-starved than most northern countries. Another well documented example is avocado production, another thirsty crop growing in warmer areas that is exported to more temperate, water rich areas (Caro et al., 2021). This also leads to a significant water footprint transfer. Coffee drinkers and avocado consumers in many water-rich areas of the world (incompatible with growing coffee or avocadoes) contribute to an economic exchange that adds pressure for water consumption from southern growing regions of the world, often aggravating water shortages in such areas. Scale issues for the water cycles are critical and clearly, efforts to improve the cycling of the small water cycle on a local scale will not offset the impacts on indirect water consumption from a large or even global scale. It is challenging to integrate the water circularity issues that need implications from local stakeholders along with impacts that can happen very short distances away that would be in the same watershed but under different government regulations, or consumer decisions that have impacts on a global scale, but little to no local impacts. There is a disconnect between the local and global cycling of water that depends on geochemical processes and environmental regulations that depend on geopolitical boundaries. 2.3. Sustainable water usage Current estimations of the water footprint provide information that is quite different from the challenge of evaluating whether a source of water is actually renewable and could be considered “circular”. Sustainable water footprint estimations are in development and must be strongly supported as one must realize that simple calculations of liters consumed do not really consider sustainability issues. In effect, one can consider that all water consumption has some impact – even capturing rain water for agricultural crop production or its own domestic usage would mean that the captured rain water will no longer be available to feed the surrounding vegetation or to trickle down to replenish surface water bodies or underground water resources. The challenge then becomes to assess whether any given activity does indeed have a significant, measurable impact upon the environment or access to drinking water by local populations, both in terms of water quantities and water quality. We could thus evaluate the impact of water consumption and the volume of water that is then removed from the system, not returned to the river or wherever it came from. This could also be applied to an agricultural or industrial activity that releases contaminants that could eventually lead to deleterious impacts on water quality without consuming any water (adding fertilisers or pesticides may contaminate surrounding waters without actually changing the water balance). An extreme example is the Aral Sea whose surface area has been reduced by 78% (Deliry et al., 2020). In such a scenario – ALL water uses that prevented the water to reach the sea would have contributed to the disaster. For the pollution side of this story – quantifying statistically significant and deleterious impacts is certainly not simple. An esti­ mation of critical loads can be made to assess the fraction of water releases that are below some concentration threshold of toxicity or 4 Environmental Development 39 (2021) 100651 S. Sauvé et al. impact for effluents – but as long as the concentrations in the water are below the threshold for toxicity - no impacts should be observed. A higher dilution capacity within the receiving water bodies can thus allow much higher releases before significant impacts are observed – acceptable releases will thus depend on the sensitivity of the receiving water body. To further complicate things – if one were to follow a river from its source downstream to the ocean – we should not consider that early releases of contaminants that had no significant impacts on the river were acceptable but that only the later releases that contribute to exceed the threshold are the culprit and responsible for the impacts. All releases that contribute to the total load are proportionally responsible for the impact – not just the last. For example, if excess phosphorus causes algal blooms in a lake fed by a river – all sources of phosphorus (along with nitrogen and other nutrients) share a proportional responsibility in causing the environmental problem. Evaluating “grey” water is also more complex due to the dual accounting of some liters of water that are consumed and contaminated – but the grey water usually represent some virtual liters of water from the river or another source that ought to be used to dilute that pollution below a specific threshold. It can become confusing to compare liters of water consumed for a product with liters of water that are further needed to dilute the pollutants. Those “pools” of water can be estimated and represented using liters of water but they are not easy to compare and really, the focus should not be on diluting the pollution but on finding ways to retain the contaminants and prevent their release to the environment. The evaluation of water that is contaminated by consumption should be maintained but should be based on actual water consumption and not on the virtual amounts of water required for dilution. When significant environmental impacts from water pollution are observed, it also becomes quite intricate and difficult to apportion who is responsible for what and really, not a single contaminant source is totally innocent as all sources share the burden of pollution. This underlines the significant challenge to cope with nutrient releases when different natural, agricultural, domestic and industrial sources all potentially contribute at varying levels to cause a problem. If the contaminant sources are across regions and subjected to different governments using different regulatory tools and mechanisms – this further complicates the efforts to find a common solution to quantify the problem and provide a strategy. The interaction of science and policy further complicates finding a solution (Y. Liu, Gupta, Springer and Wagener, 2008). How could we distribute fairly, a “sustainable” right to release contaminants within the resilience capacity of the environment to assimilate such contaminants and prevent any significant deleterious impacts? The apportionment is further complicated by the unequal strength and financial capacity of the various consumers. An innovative solution to this problem was found to address elevated salinity in the River Murray (Abel et al., 2016). Here, the objective is to meet a certain salinity target downstream (i.e., at the water intake for the most downstream user). Whilst all users (here, different sub-basins) must contribute to salinity abatement, they can do so either locally or elsewhere in the basin. Most sub-basins have invested in salinity control measures further downstream because these were more economical than achieving a similar salt load reduction locally. To allow a fair usage, water consumption rights are sometimes shared among different users. How do you apportion the small individual needs of citizens relative to the very large consumption required for agricultural or industrial purposes? Most of the water footprint estimations are for specific crops or goods and only few studies have looked at geographical variations. Thus, broad scenarios must be used to yield estimates that can be further fed into various models. Estimates of the variations in water consumption for animal production depending on location of origin could vary tremendously – for example beef production consumes an average of 15 400 M3 of water per ton of meat – but this varies from 6500 in the Netherlands and up to 16 500 in India (Mekonnen and Hoekstra, 2012). This highlights that the same product or consumer good could have a very different water footprint and a very Fig. 1. Circularity of water illustrated with examples of water transfers operating on a local and larger scales but also affected by trading of commercial goods that have hidden virtual water consumption associated to their use (not illustrated). 5 Environmental Development 39 (2021) 100651 S. Sauvé et al. different sustainability or circularity depending on where it came from and what source of water was used in its production. From a circular economy point of view – a large water footprint coming from a sustainable-renewable-closed loop system would be preferable to a smaller water footprint that would depend on a non-renewable water source. The challenge for water footprint estimations is to differentiate the “circular nature” of the consumed water. Circular economy is integrated when sustainable water footprints are being considered. 2.4. Circularity of water Fig. 1 illustrates the water cycle, including the consumptive uses that are usually associated with the water footprint. However, it also includes other processes involved in the circularity of the water cycle. This figure is certainly a simplification, but it offers an illustration of which flows correspond to water footprint estimations and which portions of such flows might actually be considered circular (or not!). Water begins with rain – this is the “green” water footprint that we would most likely expect to be circular when managed properly. Nevertheless, rainfall harvesting and land-use change can significantly impact water available through runoff from catchments and recharge rates to aquifers. There can be complex ethical issues as to who has the right to use that green water and how should we prioritize its apportionment. Indeed, the first step in defining the circularity of water is for society to make choices for what environmental goals are to be achieved. In the context of a rapidly changing world, virtually all ecosystems are impacted by anthropogenic activity to some extent, and many are in the process of ‘changing’. Thus, defining environmental objectives first involves a dose of realism about what can be achieved - what are the key ecosystem services we can and wish to maintain. The next step is to define the environmental water requirements to achieve a given environmental goal. These are unique to each ecosystem and integrate some combination of water quantity and quality. This is the ‘water regime’ for the ecosystem - the appropriate timing of flows of different magnitudes for a river, variation in pressure for a groundwater-fed springs, etc. The last step is to have strong regulation mechanisms to guarantee the agreed share to the environment. With the playing field thus set, planning to maximise the circularity of water can begin. The main components of the water cycle are included in Fig. 1, including rainfall, recharge, evapotranspiration, storage in lakes and reservoirs, and surface water and groundwater flow. Water for agri-food production and for residential or commercial activities will need to come either from rainfall, surface water, groundwater, or recycling. Thus, the water balance for the system must be well constrained before its circularity can be defined. The water balance is a moving target, with processes like climate and land-use change significantly impacting water availability through changes in runoff and recharge rates. These are not linear processes and can be difficult to predict (Fowler et al., 2016). Geographical scale is also challenging, some of the processes illustrated in Fig. 1 operate on small local scales, but some of the broader exchanges operate on a global scale, the water cycle has a total disregard for geopolitical boundaries. A hypothetical water treatment facility is also illustrated in Fig. 1 and shows that wastewater can be treated to regain its “circu­ larity” and therefore, the same goods can generate more or less grey water depending on the quality of the wastewater treatment. This also highlights that the actual water treatment process and technologies will also have an impact on circular economy. This is another example where the evaluation of circularity of water is disconnected from the mass balance of water but rather measured in terms of consumption of energy, chemicals and other consumables. The evaluation of the circularity of water will certainly depend on how we define water consumption that meets the circular economy concepts. It is probably easier to define the circularity of water by focusing on water consumption and other activities that impact grey water (not forgetting that some usages do not “consume” water but will require water to dilute out the potential envi­ ronmental impact of contaminant releases). Investing in cleaning water increases its value and encourages re-use. The circular water would thus be consumption of water that is in a closable loop, i. e, the whole process or water harvest and recuperation can be repeated ad infinitum without loss of the water resource or its contamination. From a circular economy footprint perspective – it would actually be best to calculate the total water footprint and deduct the circular footprint (which is sustainable with minimal impact) – thus yielding the non-circular, non-sustainable water footprint that we should seek to prevent and minimize. In effect, consumption of circular water should be considered as having negligible environmental impacts. Using this definition, the green water footprint arising from rainwater should be considered circular (inasmuch as local population needs for drinking water, food production and environment preservation are met). Any grey water footprint should not be considered circular unless there is a water treatment in place to remove the contaminants from the water before its release to the environment AND if the water treatment itself respects circular economy principles (main concerns are for energy and chemicals consumed to insure there are no other environmental impacts). The tricky part to determine the circularity of water will be to apportion which part of the “blue” water footprint is circular (surface or groundwater sources). Some of the blue water footprint can be maintained indefinitely but some portion is not sustainable in the long term. Sustainable groundwater use remains a challenge for many reasons, including that it is only definable over long timescales (decades, centuries or even longer). Aquifers that typically host large volumes of water are ‘safe’ in the short-term (for the next few years) but this is largely irrelevant for establishing long-term sustainable extraction limits, which are a function of the long-term recharge and discharge rates to and from the aquifer. An extreme example is fossil groundwater resources – aquifers recharged under a past wetter climate but for which there is very little recharge at present. There is no sustainable water use for such aquifers – in such situations the water is literally mined. On the other hand, some aquifers are ‘storage-limited’ rather than ‘recharge-limited’ under current conditions (their recharge potential is larger than what the aquifers can host). In this case, groundwater extraction can be partially offset by increased recharge rates (but at the expense of reduced surface flows or runoff). Managed aquifer recharge is increasingly used to store additional groundwater in aquifers when that is possible, especially when surface water storage is not possible or desirable. Unlike for surface water ecosystems, defining the environmental water requirements 6 Environmental Development 39 (2021) 100651 S. Sauvé et al. of groundwater-dependent ecosystems is in its infancy. Which ecosystems use groundwater is not even known in most catchments, let alone what their requirements are. The evaluation of the circularity of surface water harvest is complex because it is highly case-specific and dependent on the water body itself – what is happening upstream and downstream could ultimately impact the circularity of the water usage. Surface water harvest would be circular if the harvested water does not prevent or reduce the ecosystemic value of the water body (lake or river) where it comes from. If taking water reduces the water volume to hinder aquatic organisms from striving or reduce the quality of life of local human populations than it probably should not be considered sustainable nor circular. In a circular economy thinking, water-deficient environments must use all possible strategies to preserve and optimize water usage. Such strategies include optimizing irrigation usage in agriculture, recuperation of rainwater and wastewater and even reuse of wastewaters as drinking water (Angelakis et al., 2018). Wastewaters are sometime treated and reinjected in aquifers, either to be recuperated or to prevent the infiltration of salt waters in some coastal environments (Zuurbier et al., 2017). In some instances, reusing domestic wastewater for human consumption is not possible because of strong social resistance or even refusal by the community (Duong and Saphores, 2015). In some situations, this has been circumvented by using the treated wastewater for horticulture and vineyard irrigation, thus generating new industries in economically-disadvantaged areas (Duong and Saphores, 2015). Investing in water increases its value to society. In effect, in such situations, the impact of the water footprint of a given process is shared among a suite of processes as the water is reused. Rainwater used in agricultural production can become contaminated through additions of fertilizers that increase the occurrence of blue-green algae. Drinking water production needs to be adapted to prevent the breakthrough of algal toxins. Drinking water will ultimately end up in urban wastewater which can be recuperated for agricultural crops – with a portion of this water lost through evapotranspiration and a portion that is treated again and used for the production of food crops. When evaluating an underground water source, if pumping rates equal recharge, all the groundwater-dependent ecosystems associated with the aquifer will eventually die. Practically, groundwater exploitation rates tend to diminish over time in unsustainable scenarios because the water table falls below well screens, or the remaining groundwater becomes contaminated by lower quality water displaced from nearby formations. In arid climate, this often means salinization or radionuclides (radium in particular) and dissolved metals can also be an issue for fracking and other exploitation (Lagacé et al., 2018; Stackelberg et al., 2018). Fig. 1 does not illustrate desalination and this could be an overarching solution and it is indeed already being used in many arid (and relatively rich) places around the world. This is currently very costly but if we could eventually do this cheaply –we could in theory extract fresh water from the oceans and access a nearly infinite source of water. The caveats is that for this water to be considered sustainable, green and circular, we have to look at the process through which it is produced. If we eventually have access to plentiful green energy, and can make the desalination process work efficiently without excess consumables and equipment AND if the resulting brine can be disposed of without significant environmental impacts (Roberts et al., 2010). Then and only then, could we consider the desalination to be circular. There is still a very long way to go for this process to be considered green or circular. 2.5. Sustainable – circular water footprint Whilst many shortcomings of the current means of estimating the water footprint are highlighted – such challenges have been recognized and are identified as the sustainable water footprint. The objective here is to illustrate how we can better integrate circular economy concepts into the estimation of sustainable water and move beyond green, blue or grey footprints measured in liters of water. We would define the circular water footprint as water that can be harvested repeatedly with negligible environmental im­ pacts – this is certainly analogous to sustainable water use. In this context, we can think of the natural capital of water not as liters of water that are currently potentially available in the system but really as a flux reflecting the system’s capacity to provide water in a sustainable way (Wackernagel and Rees, 1997). What is really needed is to focus on the non-sustainable water footprint – a very large sustainable, circular water footprint would be preferable to a much smaller but non-sustainable footprint. It is certainly going to be challenging to refine water footprint estimates to ascertain the portion that is sustainable and circular from that which is not, but various efforts towards this are already underway. Ultimately, this should underline that we often overemphasize localised small water savings which are quite sustainable, circular and more socially acceptable at the expense of other indirect water footprints which are largely ignored and have large impacts on distant communities (and are more challenging to address). Integrating sustainability and circularity into the estimates of water footprints is an excellent means to properly assess such water consumption. Complex situations will also require the integration of the implications for circularity of water along with many other chemical or physical components, and various ethical issues. It is also important that defining sustainable use of water and its circularity will require the acknowledgements that different stakeholders have a different perspective that will change how they define sustainability and circularity of water to better reflect their interests and concerns. How do we compare a small renewable water consumption that also contributes contaminants to the drinking water source of a small village with a large consumption that has no pollution impacts? In a water-rich environment, if we take an excessively long shower, the main environmental footprint is for the energy and chemicals used for water treatment and the energy used for heating the water. From a water footprint perspective – the impact would be for contaminated water that might be generated if we used excess personal hygiene products that would not be removed by the wastewater treatment plant and hence would have some residual environmental impact. How long we stayed in the shower has little impact on the contamination of the water – it would even decrease the contamination of the water by diluting shampoo and soap into more water. If no contaminated (grey) water footprint is generated – then this would be circular from the point of view of water. Overall, this is a zero-sum game – water taken from the river is nearly all returned in nearly the same condition to the river. From a circular economy perspective, contaminants in water are lost resources that ought to be recovered and maintained in closed loops and this is inherently more complex than a simple water budget (Iacovidou et al., 7 Environmental Development 39 (2021) 100651 S. Sauvé et al. 2017). Now when we eat breakfast afterwards, the water footprint will be much higher because of the water used to produce the food we eat. If I live in a northern, water-rich environment, local food products would be likely to have been produced using water that could be considered sustainable and circular but we would need to scrutinize agricultural practices to properly estimate grey water production. If I eat imported food coming from a warmer climate (coffee, for example), I would need to estimate potential water pollution but I would need to be especially vigilant and ascertain the fraction of agricultural irrigation water that came from a non-renewable source. The daily consumption of water for shower that is mostly renewable has but a small probably circular local water footprint whereas the daily consumption of food could potentially have a much larger potentially non-circular, non-sustainable global water footprint. It therefore seems critical to focus water footprint guideline improvements to integrate such estimates. This also means that we will be comparing liters of water from different environments that will have different footprints for the same volume of water consumed. Scales are also critical, local accounting could have different socioeconomic or political objectives than larger scale global accounting of sustainable use of water and its circularity. There are certainly strong political forces that will want their say in how we define sustainability use and circularity given the large associated socioeconomic impacts. 2.6. Promoting circular economy for water The first step in promoting sustainable water usage is to better identify which systems use water in a sustainable manner and which portion of water usage is not sustainable and circular. This means that the blue, green and grey apportionment of water would need to be further subdivided to identify the “dark” side of each such fraction. All contaminated (grey) water is by definition not circular and not sustainable and already being considered into the water footprint (albeit the currently proposed estimations of grey water could certainly be improved to integrate a wider range of potential contaminants). Provided proper water treatment, the status of grey water could actually be improved and the footprint reduced or eliminated. Rainwater (green) can probably be considered in most situations to be sustainable and circular (albeit this would need to be confirmed). Estimation of blue water consumption (surface or underground water) must be refined to apportion what fraction is not used sustainably. This “dark” blue water will not be easy to estimate. In terms of public policies, one of the ways to promote the circular economy of water is to internalize environmental externalities. By integrating the actual effects of the loss of water quantity or quality into the analysis and decision-making processes, we can have a better understanding of the situation. In this sense, some types of programs and policies are moving forward with this idea, notably the payment for ecosystem services programs. These programs develop in many forms: from regulatory frameworks to financial incentives, to integrated approaches. The recognition of the value of water can be developed by the constraint of normative frameworks such as the water fee for companies that use water directly (e.g. bottling of water or manufacture of drinks) or indirect (e.g. extraction of oil or gas, manufacture of pesticides, fertilizers and other chemicals). This internalisation of a “free” resource is closer to the polluter-pays principle than to a real sustainable development process and represents a minimal step towards the recognition of natural processes in the economy. Moreover, the fee rate varies drastically from one region to another, depending on a series of actors, including the availability of the resource. For example, in the Canadian province of Quebec, where water is abundant, the expected water fee for industrial users range between 0.0025 and 0.07 $/m3, while in other Western countries where the resource is less abundant, this fee is higher, as in Italy ($0.2/m3) or in Denmark ($1/m3) (Environnement et lutte aux changements climatiques, 2019). In recent years, there has been a tendency to encourage the creation of incentives for various resource users and managers to reduce their environmental footprint on water. Among the long list of models for payments for ecosystem services, Water Quality Trading schemes have developed as an interesting avenue, mainly when looking at issues related to diffuse pollution. In these types of marketbased mechanisms, but often with a hybrid government presence (Sattler et al., 2018) participants can voluntarily exchange water quality credits or pollution rights. Relatively popular in the agri-environmental sector, they address a water pollution issue by providing new sources of financing for farmers and more flexible governance. Among the existing programs, the Total Phosphorus Management Program of the South Nation Watershed in Ontario (Canada) aims to achieve a net improvement in water quality using a 4: 1 exchange ratio. Thus, for each additional kilogram of phosphorus emitted by a point source of pollution, 4 kg must be compensated within the watershed by the implementation of agri-environmental practices (O’Grady, 2011). This hybrid market system is based on a normative government framework (regulating credits, environ­ mental objects and participants, among others), but with a market principle administered by an NGO. Many other examples of these hybrid markets are developing, but the main gap they present is the lack of biophysical foundation of their objectives. In fact, due to the complexity of the functioning of agroecosystems and diffuse pollution issues, it becomes difficult in these cases to measure and monitor the effect of the measures taken on the health of the watershed (Tabaichount et al., 2019). Beyond these incentive or normative approaches, the application of circular economy frameworks to water forces us to recognize the complexity of socio-ecological systems. This framework requires that we embrace the biophysical dimension of the resource, but also the economic, political, social and institutional aspects. The scientific literature shows some successful cases, mixing this diversity of actors within a complex socio-ecological system. One of the classic cases is that of Vittel (Nestlé Waters - France), a water bottling company that has jointly set up a payment model for ecosystem service based on the restoration of the resource. It is deployed to reward farmers present in the watershed so that they adopt more sustainable technologies and practices (Perrot-Maître, 2016). The design of circularity models, as well as their application, represent challenges that must mobilize a wide range of actors within the same territory. 8 Environmental Development 39 (2021) 100651 S. Sauvé et al. 2.7. Conclusions We may have seemed to be criticizing water footprint estimate but on the contrary – we welcome the impact water footprint es­ timates have had to better focus on indirect water consumption. The main objective is to highlight that water footprint estimations must focus less on the blue-green-grey categorization and move to the next step to estimate circular water footprint (or actually focus on non-circular, non-sustainable water consumption). It is also critical to move away from simple estimate of liters of water consumed but broaden from a water footprint to an environmental footprint that would integrate broader indirect impacts such as pollution, energy consumption, consumables for treatment, etc. We must identify which water consumption is sustainable and which portion of our water consumption has an environmental footprint that is actually non-sustainable and non-desirable. This will allow us to better target initiatives to reduce the water consumption that has the most damaging impact upon our environment. Circular economy should then be used to implement the proper market initiatives or tools to minimize the environmental footprint of water consumption. 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