Despite the growth in water security literature, few papers link it to water justice. Using the Water System Justice (WSJ) framework, which builds on Earth System Justice (ESJ) (Gupta et al., 2023a, 2023b), we re-examine what water security could mean. Grey and Sadoff (2007, p. 545) define it as “the availability of an acceptable quantity and quality of water for health, livelihoods, ecosystems and production, coupled with an acceptable level of water related risks to people, environment and economies.” Water security is often seen in nexus to food, energy and health security (Pahl-Wostl et al., 2016a). While water security simply means adequate access needed by a society for all its key functions, water securitization refers to how water scarcity becomes ‘securitized’ through language, the military, and maps to become a threat (Fischhendler and Nathan, 2016).

Against this background, we ask: how does Water System Justice redefine the content of water security in the Anthropocene? We link local to global water security with WSJ to show that justice means ensuring security in a systemic context, not securitization, and requires unprecedented cooperative behavior between states and people. This perspective paper recognizes that “any operationalization of water security must be negotiated in a societal discourse” (Pahl-Wostl et al., 2016b, p. 4), but proposes conceptualizing and operationalizing water security through a Water System Justice lens.

Since “water security problems must be tackled at different and often simultaneously at multiple scales” (Pahl-Wostl et al., 2016b, p. 8), this fits well with a WSJ approach that builds in local to global justice implications. At the global (to local) level, WSJ defines the safe and just ‘corridor’ for human interactions with relevant water boundaries and standards.

Operationalizing the 3I’s to minimize significant harm to people, ecosystems and Earth system stability promotes a stable water system including water based ecosystems. Based on 4 years of research, the Earth Commission proposed that: (a) surface water fluctuation should not vary more than 20% in relation to the natural flow level on a monthly basis; and (b) groundwater extraction should not exceed its recharge rate (Rockström et al., 2023, p. 107). Groundwater boundaries also avoid land subsidence and saltwater intrusion (Gupta and Conti, 2017). Debates about the underlying data and methods has also been settled (Bunn et al., 2024). Both these boundaries have been crossed at local to global levels: 47% of groundwater levels are declining, and 34% of surface water bodies fluctuate more than 20% (Bunn et al., 2024), while the minimum water needs and water for food, energy and infrastructure needs were not met for the poorest (Rammelt et al., 2022). Additionally, a safe boundary for green water terrestrial precipitation, evaporation, and soil moisture—“represented by the percentage of ice-free land area on which root-zone soil moisture deviates from Holocene variability for any month of the year” (Wang-Erlandsson et al., 2022, p. 380), has also been crossed.

These boundaries are based on literature, Earth system modelling, historical data, and expert judgement and data gaps, especially in developing countries are accommodated by employing proxies like recharge rates and flow fluctuations. These quantitative boundaries are complemented with quality standards, e.g., emission, technology and ambient standards for water bodies (Rockström et al., 2023). Existing standards (WHO, EU and others) fall short of what is needed for the new chemicals (e.g., PFAS), minerals and metals. Boundaries and standards need to be contextualized for relevance and restrict water use, consumption, and pollution.

The climate boundary affects water security as climate change causes droughts, floods, changing rainfall patterns and melting glaciers. For every 1°C rise in global average temperatures, there is a 7% increase in the moisture-holding capacity of the atmosphere, exacerbating weather extremes (GCEW, 2024). The safe and just boundary for climate change is 1°C above pre-industrial levels (Gupta et al., 2024b) which exposes tens of millions of people to irreversible harm, is a threshold that has already been transgressed. Agriculture uses 70% of all blue water as well as green water, and pollutes water through N and P inputs, leading to eutrophication and health risks. This requires safe and just boundaries for nitrogen (N) and phosphorus (P) surpluses by capping nitrogen surplus at 61 Tg N per year and phosphorus at 4.5–9.0 Tg P per year in cropland areas to prevent nutrient leaching (Rockström et al., 2023).

These quantitative and qualitative boundaries represent the upper limit. The lower limit is defined by the impacts on the water system of meeting the human right to water and sanitation (HRWS) which requires approximately 50 to 100 liters of water per person per day (WHO, 2017), although this rises to about 4,000 liters per person for a dignified life when food, domestic and industrial needs from blue and green water are considered (GCEW, 2024). These minimum needs have been calculated using the same units as the boundaries and enables the definition of a safe and just corridor (Gupta et al., 2024a).

Thus, at global level, water security can be operationalized using WSJ which reinforces the need for global cooperation (see Figure 1). The water, climate and nutrient boundaries and quality standards represent the maximum allowable pressure on the water system. The pressures of meeting the minimum needs of all is the foundation. The water within the corridor needs to be fairly allocated including responsibilities for harm and risk. Thus visualizing the hydrological, climate and nutrient cycle as a global common good and meeting minimum needs as a merit good provides additional reason to enhance multilateralism and coordination to regulate water and pollution allocation mechanisms through the polluter pays principle and the common but differentiated responsibility principle. This ensures sustainable and equitable water use, fostering international cooperation for the collective good. Moreover, trade in water and embodied water (virtual water trade) needs to be undertaken within multi-level water boundaries, standards and foundations. Finally, land and water grabbing by foreign investors (e.g., miners) needs to be avoided in line with the ‘Means’ of Earth System Justice (Bosch and Gupta, 2022; Rulli et al., 2013).

Transboundary water security concerns emerge when water resources cross (sub)national boundaries. Our surface water boundary requires that water flows downstream and into the oceans, and that monthly withdrawals are in line with recharge levels while pollution needs to be within ambient standards for water. As a foundation, the needs of local people have to be met first. The remaining water in the corridor is what can be equitably shared between transboundary riparians.

These boundaries and floors challenge the existing 800 or more international, freshwater-related agreements on the 313 international river basins (Oregon State University, 2023) and require rethinking shared aquifers and account for green water flows. Upper riparians have been unwilling to share water, as demonstrated through the limited ratification of the Watercourses Convention (39 countries) and the Water Convention (55 countries¹) (Gupta, 2016). Where water scarcity is acute and increasing with climate change, countries are securitizing water using hardline diplomatic stances including militarization and conflict (Fischhendler, 2016). Securitization undermines social and environmental justice goals ignoring downstream communities and ecosystems (e.g., Palestinians in the West Bank) (Nathan and Fischhendler, 2015).

A WSJ approach at the transboundary level implies that water security requires meeting minimum quality and quantity standards for humans within the safe and just water and related boundaries which leaves water for nature to flourish (interspecies justice). This entails ensuring downstream countries and marginalized groups receive fair access to water resources, and that agreements account for the short and long-term sustainability of water resources (intra and intergenerational justice).

Fortunately, strategic ‘realpolitik’ and justice approaches are not necessarily mutually exclusive, as countries are interdependent on the hydrological, climate and nutrient cycle (GCEW, 2024) and unification behind WSJ goals can open the door to less ‘zero-sum’ approaches to transboundary water cooperation. While the historical reluctance of states to cooperate on blue water challenges such optimism, green water flows provide a compelling basis for more cooperation especially since nearly half of all precipitation over land originates from terrestrial sources (Petrillo et al., 2024). Atmospheric moisture flows connect regions making them highly interdependent: e.g. Brazil’s Amazon rainforest recycles 36% of its own rainfall, while also exporting significant moisture to neighboring countries, thus contributing to regional/transcontinental precipitation (Smith et al., 2023). Similarly, West African evaporation contributes to rainfall in South America. These interconnections underscore shared dependency and need for cooperation.

This interdependence suggests that aligning national interests with WSJ principles could open pathways for less zero-sum approaches and reduce the adversarial nature of transboundary water negotiations (Tuinenburg et al., 2020).

From the national to local levels, water security issues become more immediate and tangible with competition between different uses and users. Agriculture uses 70% of water abstractions and water utilities that provide quality water to homes and offices account for ~10%. Such water must be returned clean to nature. Indigenous groups and environmental rights activists are advocating for sustainable water governance practices including legal personhood of rivers and other water bodies (e.g., Embassy of the North Sea) (Cyrus, 2020). When such locally rooted customs are recognized at the national level, they can ensure that water bodies are treated as ecological systems, in turn shoring up water security. The 20% fluctuation rule (see 3.1) could be seen as a way to define the right of the river.

Many states use a priority of use system to guide water access and allocation, especially in times of scarcity. This can ensure that achieving minimum human (HRWS) and nature needs is made actionable, as human consumption and adequate environmental flows are afforded top priority, followed by uses such as agriculture (which itself must differentiate between vital and luxury goods, such as export crops) and industry (AI creates a new problem because of its enormous use of energy, water, and minerals/metals) (Gupta et al., 2024). The priority of use must be sensitive to local needs and could be linked to pollution permits.

At national level, increased water scarcity can lead to securitizing water by promoting full permanent sovereignty over natural resources. Water markets may lead to water hoarding (as in Chile). When water is commodified, the state/businesses may prioritize uses with higher returns (e.g., industrial over agricultural, urban over rural) at the expense of marginalized communities and ignoring sacred relations with water (Taylor et al., 2019). For example, Gaybor (2011) in Boelens et al. (2018a) found that in Ecuador the agricultural export sector represents 1% of farms while receiving concessions for 67% of the total available irrigation water. Securitization by international investors happens through land and water grabbing (Franco et al., 2013), the building of infrastructures (e.g., dams), as well as through investor-state contracts (Bosch and Gupta, 2022) and putting water as an asset on companies balance sheets. These can exacerbate local insecurity. A justice-centered approach to water security addresses inequalities, recognizes diverse relationships to water, and moves beyond a sovereign technocratic and financialization model of water securitization. Operationalizing just water security nationally requires contextualization, which involves incorporating justice-based conditionalities to contracts, concessions, permits, licences, EIAs, policies, strategies, rights, investment agreements, land planning, and Corporate Social Responsibility Programmes—putting justice front and centre.

In this perspective paper, we conclude that ‘water security’ can benefit from ‘Water System Justice’ and its operationalized quantifications as developed by the Earth Commission. This requires that water security: accounts for recognition and epistemic justice, and plural ways of knowing water (Wilson et al., 2019); incorporates the 3I’s of justice—Interspecies, Intergenerational and Intragenerational justice in boundaries and standards; meets minimum needs, and holds polluters accountable, and challenges state and private interests that threaten access to clean water. It additionally supports local communities’ right to procedural justice.

Such boundaries can contextualize Earth Commission boundaries and international quality standards. This forms the upper limit of the local to global level corridor. The pressure on the water system of meeting minimum needs to water, including water for food, energy, infrastructure, calculated using the same units as the boundaries provides the foundation. The remaining water in the corridor in between, then needs to be reallocated between the different uses and users in an equitable and optimal manner. Incorporating green water boundaries and the flows of atmospheric rivers adds another complex dimension to water security. Addressing power and the drivers of inequality requires justice principles. A commitment to collaborative management, rooted in WSJ principles and proposed quantifications, is essential to balance human and ecological needs for a secure and just water system. The scalar dimension of water security can be linked to the multi-level systemic justice approaches. Scale jumping, e.g., where local level values match global ones but not national ones can be used to reinforce justice especially by linking key shared justice principles. The interdependence between countries reinforces the need for just cooperation for collective security.