15.1 Introduction

The attention of philosophers to water is of recent date. While the flow of water as a metaphor for life goes back to the pre-Socratic philosophers (cf. the well-known quote panta rhei – everything flows, often attributed to Heraclitus), the importance of water for life – and with that its essential role for both humans and nature more generally – has received little attention in the normative philosophy literature before 2010. This is surprising as the different and often competing water uses, the exhaustion of the earth’s freshwater resources, and the effect of flood-prevention strategies on water availability and water quality pose questions that are deeply normative and by that in the heart of philosophical disciplines such as political philosophy, philosophy of risk, and ethics. Since 2010, maybe as a result of increasing attention to climate change, the topic of water is gradually receiving attention in the philosophical literature, focusing primarily on these normative questions and therefore often discussed under the label of water ethics (Doorn Reference Doorn2019; Meisch Reference Meisch, Springer and Grimm2018, Reference Meisch2019).

This chapter aims to explore how the planetary boundaries framework can be useful for thinking about water-related risks complementary to frameworks developed in the philosophical literature on water ethics and risk ethics. Hence, the aim is not to criticize or further refine the planetary boundaries but rather to see how the philosophy literature can benefit from the framework and vice versa. To do so, I highlight three points from the water ethics and risk ethics literature that are particularly relevant to our thinking about the water planetary boundary. The first concerns the division of labour between science and management, the second concerns the multitude of water-related risks and risk-risk trade-offs, and the third concerns the metric of intergenerational justice in water policy and engineering. By discussing these three points, I show how the planetary boundaries framework can play a role in water-related management and policy decisions. In the concluding Section 15.5, I reflect on the role of water ethics in these decisions.

15.2 The Reception of the Water Planetary Boundary in the Literature

The water planetary boundary is one of the nine boundaries that, taken together, propose quantitative limits for human perturbation of critical earth system processes (Rockström et al. Reference Rockström, Steffen and Noone2009). With the concept of planetary boundaries, Rockström and colleagues have developed a framework that can be used to demarcate a safe operating space for human activities. It is important to stress this goal: it is intended to develop the safe operating space itself, not the distribution within that space. The water boundary was originally labelled ‘freshwater use’, and in the early publications, it was formulated globally in terms of the maximum rate of consumptive use of blue water (Rockström et al. Reference Rockström, Steffen and Noone2009). In later publications, the boundary was further refined with a limit at the basin scale as well, formulated in terms of maximum monthly withdrawals as a percentage of mean monthly river flow (Steffen et al. Reference Steffen, Richardson and Rockström2015).

In recent years, the framework has received some criticism: some points of criticism are warranted and also accepted by the initiators of the framework, but some points of criticism also seem quite unfair. One rightful point, which could also be read as a modest revision or refinement of the water planetary boundary, is the metric of the boundary – and in a way also the label itself. As stated earlier, it was originally formulated in terms of blue water consumptive use, because Rockström et al. considered this a good proxy variable for the planetary limit, integrating the three largest anthropogenic manipulations of the water cycle: human impacts on precipitation patterns, modifications of soil moisture by land use and land cover, and water withdrawals from discharge for human use. In a later paper, it was suggested to move away from human water use as a metric and to conceptualize the water planetary boundary as ‘stores of the water cycle’ (Gleeson et al. Reference Gleeson, Wang-Erlandsson and Zipper2020). The reason for this move is that ‘the foundation of the planetary boundaries framework is the Earth System and, in the case of water, the Earth System functions of water’ (231). It makes indeed much more sense to express the boundaries in terms of geophysical variables directly related to this boundary (i.e., water stores) and not in terms of some indirect and aggregated variables like water use. In this later paper by Gleeson et al. (Reference Gleeson, Wang-Erlandsson and Zipper2020), which includes most of the original authors of the Rockström et al. (Reference Rockström, Steffen and Noone2009) paper, the authors carefully avoid the term ‘freshwater use boundary’ and replace it with ‘water boundary’. In this chapter, I will use this more recent label ‘water boundary’.

A different line of criticism comes from authors who attack the framework for not paying enough attention to contextual factors, including technological interventions and governance concepts (Bogardi et al. Reference Bogardi, Fekete and Vörösmarty2013), failing to consider questions of equity (cf. Steffen & Stafford Smith Reference Steffen and Stafford Smith2013), and insufficiently recognizing the impact of impaired water quality on the water system (One Earth 2020). With the changed focus from freshwater use to water stores, especially the reference to technological interventions does no longer seem apt. While these interventions may help us stay within the boundaries, they do in principle not affect the boundaries themselves.

Regarding equity, indeed, the planetary boundaries framework is not enough for resolving all issues. However, given the goal of the framework (‘to provide the safe operating space’), this incompleteness is not problematic per se and could even be considered a strength. The framework is not intended as an allocation framework but rather as a set of constraints – or at most as a partial allocation framework – spanning the space within which allocation can take place. As such, the model fits quite well in the traditional division of labour between science, on the one hand, and management or policy, on the other, as promoted in most of the risk literature. Of the points of criticism mentioned, the lack of attention to water quality issues seems the most serious one.

To gain more insight into how the planetary boundaries framework in general, and the water boundary in particular, can complement water ethics and risk ethics and vice versa, let us turn to some ethical perspectives on water-related risks.

15.3 Ethical Perspectives on Water-Related Risks

Until a decade ago, no subfield within applied philosophy explicitly dealt with water (Doorn Reference Doorn2013). Even though environmental ethics had developed into a solid field by that time (Jamieson Reference Jamieson2008), it was less concerned with the questions that are typical to water: the risks of water shortage, poor quality water, and inadequate flood protection, as well as questions of distributive justice related to these risks, and the importance of water for other sectors (Brennan & Lo Reference Brennan, Lo and Zalta2022). Around that time, the concept of water security emerged in the water literature as a lens through which to look at these questions (Lankford et al. Reference Lankford, Bakker, Zeitoun and Conway2013: ix; see also Cook & Bakker Reference Cook and Bakker2012; WaterAid 2012). Water security explicitly recognizes the interdependencies between different water-related risks and does not exclusively focus on either reducing water scarcity or water pollution, or on improving safety from flooding. This water security perspective allows us to move beyond water scarcity as an issue of competing water uses and allocation. It shows that it is also about decision-making, rights, distributive justice, and who has a say. Yet, this literature is still disconnected from the relevant philosophical literature.

In recent years, philosophical perspectives on water-related risks have been developed (cf. Doorn Reference Doorn2019; Meisch Reference Meisch, Springer and Grimm2018, Reference Meisch2019). In this section, I highlight three points that are particularly relevant to our thinking about the water planetary boundary. The first concerns the division of labour between science and management, the second concerns the multitude of water-related risks and risk–risk trade-offs, and the third concerns the metric of intergenerational justice in water policy and engineering.

15.4 Distribution and Allocation within the Boundaries

In The Division of Labour between Risk Analysis and Risk Management, we saw that the planetary boundaries framework fits in the traditional division of labour between risk analysis and risk management, or between science and policy in more general terms. The framework provides the safe operating space, but it does not provide guidance on how things should be allocated within those boundaries, and this is sometimes also mentioned as a weakness of the framework: given how small the remaining safe operation space is, does this planetary focus not come at the expense of vulnerable people currently alive (cf. Rammelt et al. Reference Rammelt, Gupta and Liverman2022)? Water ethics and political philosophy more generally can provide a valuable contribution here, conceptually as well as normatively. In political philosophy, a distinction is sometimes made between distribution and allocation (Rawls Reference Rawls1971), a quite technical, but yet relevant, distinction in the context of water. Distribution is concerned with the conception of society as a fair system of cooperation over time, and it is judged on whether it delivers the outcomes that people can expect based on being part of society. In that sense, the people have certain rightful claims. Allocation and relatedly allocative justice apply when a given collection of goods is to be divided among definite individuals who do not have a prior claim on the things to be divided because these things are not the product of their work nor do these individuals stand in any existing cooperative relations. Water ethics is particularly well-equipped to help our thinking about the appropriate rules for distribution and allocation. In the case of allocation, Rawls suggests allocation according to a utilitarian principle, but other allocation rules are also possible. However, in the context of water, more important than allocation is distribution. Water is essential for life, and when it comes to people’s basic needs, such as the water needed for drinking water and sanitation, we are dealing with questions of distributive justice. Here, many people defend a sufficientarian, prioritarian, or egalitarian distribution. Making it a matter of allocation seems at odds with basic human rights, such as the right to water or the right to sanitation. The same applies to the valuation of water other than in terms of direct use value, for example, the spiritual value of water. Water ethics is well-positioned to distinguish allocative questions from distributive ones and to develop corresponding conceptions of justice. This is typically something where water ethics can complement the planetary boundaries framework. In areas where basic needs are met and there is no competition for water, it is less controversial to look at the resources as an issue of allocation. As such, distributive justice in combination with the planetary boundaries framework together provides the space within which there is room for allocation.

15.5 Concluding Remarks

In this chapter, I briefly discussed three ways in which the planetary boundaries framework and the water boundary in particular can contribute to water ethics and risk ethics. I showed how the planetary boundaries framework provides a valuable contribution to ongoing discussions in the water ethics and risk ethics literature. Vice versa, water ethics and risk ethics can also contribute to the application of the planetary boundaries framework in practice.

Some points still need further development. The current framework focuses very much on freshwater, even though it has been renamed ‘water boundary’. So far, the relation with water safety, that is, safety from flooding, is not well-established and also water quality seems underdeveloped. For safety from flooding, a stronger link with the land system change planetary boundary could be established. The land system boundary currently focuses on cropland and forestry, but this boundary may require a more fine-grained operationalization to account for the impact of flood protection strategies on, for example, wetlands and brackish deltas.

Concerning water quality, the water boundary was originally expressed in terms of blue water use, that is, the use of groundwater and surface water for irrigation or processing (Falkenmark Reference Falkenmark2003). It did not account for the use of infiltrated rainwater (evaporation) for growing crops (green water), or for the effect of water pollution (grey water), which accounts for water use as a result of pollution (Chapagain et al. Reference Chapagain, Hoekstra, Savenije and Gautam2006). This was also recognized in the report written for the European Environment Agency (Häyhä et al. Reference Häyhä, Cornell, Hoff, Lucas and van Vuuren2018), which mentioned the need to account for green water use and its interactions with other boundaries, as well as water quality constraints (expressed as grey water). As explained in Section 15.2, in the most recent revision of the planetary boundaries framework, the research group no longer talks about the freshwater use boundary but about the water boundary instead, and by that, they have also included green water (Gleeson et al. Reference Gleeson, Wang-Erlandsson and Zipper2020). The reason for not including water quality is that water quality, like marine systems, is related to other planetary boundaries, such as ocean acidification, biogeochemical flows, climate change, and novel entities. Including it also in the water boundary would lead to duplication, according to Gleeson et al. (Reference Gleeson, Wang-Erlandsson and Zipper2020). Given that many interventions in the earth system involve several boundaries, water quality is not unique, and as long as boundaries are not assessed in isolation but comprehensibly, this choice by the authors seems justified.

To conclude, as explained in the introduction of Section 15.3, the framework is criticized as not being as objective as it claims to be and, indeed, the boundaries do not follow automatically from science. Yet, given the devastating environmental impact of many human activities, the earth – including its water stores – is probably better served by the precautionary approach promoted by the planetary boundaries framework than by the optimism about technological interventions described by Bogardi et al. (Reference Bogardi, Fekete and Vörösmarty2013). The planetary boundaries framework may exactly be the framework that allows us to distinguish naïve technofixes from sustainable solutions to leave a liveable planet for future generations.