In the majority of cases, there is a positive perception of, and a level of high support for, the overall idea of water use as an alternative water source. This might be due to growing scarcities and stresses on water resources. For example, regions experiencing recent droughts are more likely to support reclaimed water (Garcia-Cuerva et al., 2016). Key institutional water stakeholders (e.g., managers, researchers or bigger users, etc.) regard water reuse highly (Chen et al., 2015a). There is an increasing receptivity towards recycling water, and this is especially true for non-potable purposes and in developed regions of the world, e.g., in Europe (Smith et al., 2015). In particular, wastewater reuse is supported by many stakeholders as an important option for water supply augmentation (Duong and Saphores 2015). However, being for or against water reuse might be a misleading “thin narrative”, which needs to be replaced by a more nuanced understanding of individual stances on recycled water (Ching 2016). Furthermore, public responses can be unstable and susceptible to change in the wake of contamination accidents, public debates, rumors, media reports, etc. (Russell and Hampton 2006).

Acceptance of water reuse decreases in cases of close-to-person uses such as bathing, cooking or drinking. This similarity pattern emerges across acceptance case studies (Fielding et al., 2018). Despite the complexity of individuals’ attitudes to contacts with reused water, the less favorable view of close-to-person contacts is stable across locations and users (Chen et al., 2015a). For example, farmers surveyed in Jordan reported a negative opinion on touching reused water or using it for fruit and vegetable cultivation despite the perceived benefits for soil productivity (Carr et al., 2011). Similarly, in Iran, the acceptance of non-personal use of treated wastewater was much higher than for close-to-person uses; e.g., 87% acceptance for public consumption such as landscaping or firefighting vs. 8% for cooking or drinking (Baghapour et al., 2017). Similar attitudes are found in Latin America, e.g., Chile (Segura et al., 2018). This is due to many reason such as the famous “yuck” effect of coming in contact with previously “dirty” water (Duong and Saphores 2015; Wester et al., 2016). This attitude of negativity or disgust can be psychologically, culturally and/or socially constructed; e.g., influenced by the media (Ching 2010). It can also be linked to a complex set of individual and contextual factors, or what Bennett et al. (2010) called “fright factors”, which include issues such as risk exposure and distribution, the level of damage and the level of trust in others and in public and civil organizations. However, ever since the beginnings of research on public attitudes during the 1960s and 1970s, the decrease in acceptance with close-to-person use has been a stable observation that is less affected by psychological or water price factors (Baumann 1983).

Awareness and knowledge on water quality and associated risks of water reuse seem to be low across regions. This finding is combined with a high demand from consumers for more information. This is because knowledge of water recycling processes has been confirmed to be quite low across cases (Fielding et al., 2018). Hurlimann and Dolnicar (2016) found knowledge about recycled and desalinated water to be low across all nine surveyed locations and suggested a higher communication and engagement level with communities. Similarly, Buyukkamaci and Alkan (2013) reported a high demand by 375 respondents in Turkey to be told more about the health and food safety impacts of water reuse. In Jordan, farmers’ perceptions did not correspond to the water quality delivered to their farms (Carr et al., 2011). In reality, awareness of health risks is generally low across many surveys of farmers in other locations (Keraita et al., 2010). While low awareness is a salient factor in many surveys, it does not apply to some location such as in Singapore where engagement with the community, the media and the public seems to be relatively high (Lee and Tan 2016). There, the attitudes towards water reuse are more influenced by economic interests, ecological limitations and national security rather than by norms or information (Ching 2016).

Water reuse acceptance varies with different water sources and reuse purposes. While acceptance decreases with close-to-person uses, the exact preference order is dependent on the location and the characteristics of the water presented to consumers. Hurlimann and Dolnicar (2016) found that rainwater is more often preferred to desalinated water for the least personal uses (garden watering and toilet flushing), but the differences in the preferred source depend on the purpose use and vary in certain locations. In fact, water originating from desalination (i.e., reused seawater) is widely accepted in many parts of the world for all types of purposes including DPR. Desalination is the main source of domestic water in GCC countries, while it is also used to a limited extent in agriculture (Aleisa and Al-Zubari 2017). In Australia, the factors behind the likelihood of using desalinated water can be similar to those behind the likelihood of using recycled water (wastewater) (Dolnicar et al., 2011). However, this conclusion is site-specific, since accepting one resource type does not automatically indicate a higher willingness to accept other types. In the GCC region, for example, wastewater reuse in agriculture is largely not accepted or practiced despite the overwhelming endorsement of desalination (Brown et al., 2018).

The consumer perception of the quality and health risks of reused water for a specific purpose is affected by other factors beyond the water source (location of collection), use purpose, or treatment technology. For example, Menegaki et al. (2009) found that labeling treated wastewater as “recycled water” would increase its use acceptance. Inaccurate labels such as “toilet to tap” (T-to-T) are used by opponents of water reuse to scare potential consumers. At the same time, events including public figures drinking beer brewed with reused water can help overcome the “yuck factor” (Katz and Tennyson 2018). Figure 1 explains how acceptance of water reuse usually changes with the source and the use purpose of such water. Here, brackish water is understood as being water from lagoons or collected from rain, while greywater is the collected and treated wastewater gathered at household level. The collection source differs, but all water sources need a high level of treatment (e.g., tertiary treatment) to be used for most purposes, especially the close-to-person types.

Factors that can increase awareness, acceptance, and trust of water reuse schemes are site-specific; e.g., education, religion, role models, media coverage, etc. The contribution of these specific factors to increasing awareness and ultimately acceptance of water reuse has been reviewed by Fielding et al. (2018), Hurlimann and Dolnicar (2016). Empirical studies show the importance of local conditions, while results are mixed for all determinant categories. One reason for the mixed results might be the heterogeneity of methods and the vagueness of the measured conceptual objects; i.e., whether studies seek to determine the incidents/perceptions/risks related to acceptance, or simply the attitudes of individuals, communities, stakeholders, or the public.

Among the many determinants of awareness and acceptance and despite the inconsistent results across all studies, education, economic and climatic factors seem to stand out in large acceptance surveys, while some other factors can be less substantive factors. These three factor groups (economic wellbeing, education and climate) were the most influential in a survey with 2,800 people in the United States by Garcia-Cuerva et al. (2016), while sex, age, location and the last monthly water bill showed no significant effect. Robinson et al. (2005) show that both men and women in the United States view wastewater reuse for personal uses unfavorably, while high income and education can lead to having greater knowledge on water reuse. Menegaki et al. (2007) showed in the case of Creta, Greece, that factors influencing willingness to reuse water are related to scarcity condition, information and awareness, income, and water price, but that age and sex still played a role. Gender did not, however, play a significant role in surveys in Turkey (Buyukkamaci and Alkan 2013). Aitken et al. (2014) found that demographic factors such as the membership of the Muslim community can lead to less support for water reuse in South-East England, while religion was seen not seen as a limiting factor in the study in Jordan (Carr et al., 2011).

Another often-cited determinant of awareness is the media. Buyukkamaci and Alkan (2013) identified the media as the most important method for informing the community. However, Goodwin et al. (2017) found that media coverage of a proposal to introduce IPR in London (United Kingdom) had no impact on online public reaction. In the case of Australia and New Zealand, Crampton et al. (2016) founded the media to be the least likely information source on drinking water quality for the respondents and stressed the role of expert knowledge, technical plans, and the involvement of communities. Similarly, Dolnicar et al. (2011) did not find any influence of TV watching on attitudes towards water reuse and stressed broader issues such as perception and prior knowledge.

A key discussion in water acceptance experiences is related to risk perception of recycled water. Risk perception and risk factors differ from location to location. This is also true for trust in public authorities to mitigate and adapt to these risks. Such authorities are largely behind large-scale, technical and centralized water reuse projects (Meehan et al., 2013) and their (lack of) competence is a key factor in assuring the public of safe water reuse. Doria (2010) examined risk and acceptance variables of water reuse and emphasized individual factors related to risk perception as well as contextual factors such as the supply system in general, trust in the suppliers, quality of information provided by media, and public trust. Crampton et al. (2016) found risk perception to be significantly correlated with employment status and sex, with location being insignificant in the case of New Zealand and Australia. Dolnicar et al. (2011) reviewed acceptance surveys and identified trust in the authorities as a key category for determining acceptance. Similarly, Fielding et al. (2018) identified risk perception and trust among many “psychological” factors of acceptance surveys, alongside other issues in this broadly defined category such as social norms, fairness, disgust, environmental issues, knowledge, etc.

The acceptance of water reuse cannot be separated from local factors such as the specific potential depending on available water resources, the exposure to certain forms of water reuse and the reuse practicability in terms of associated costs of treatment and distribution. In some regions, some water sources might be more accepted due to scarcity conditions, and awareness of water scarcity can even increase the likelihood of accepting water reuse (Dolnicar et al., 2011; Fielding et al., 2018; Scruggs et al., 2020). In regions of water abundance, some water sources such as desalination might not be accepted. Other regions have a different acceptance pattern due to differences in resource availability. In the GCC region as an example, desalinated water is largely accepted as it supplies more than 90% of domestic and industrial needs in the region, but it is too costly for irrigation (Brown et al., 2018). In this region, brackish water is available in limited amounts in some cases and can be used for recharging ground water and then reused for drinking or agriculture. Produced water is significant in the oil and gas industry and can be utilized locally or provided in limited amounts for least-personal uses. Greywater represents a high potential due to the very large water use footprints per capita in the region, and it could be reused in the future on a household level for recreation or agriculture. Wastewater reclamation is expanding and is used for all kinds of purposes such as landscaping or aquifer recharge (Aleisa and Al-Zubari 2017). Finally, acceptance of certain water types can be high in urban areas. For example, in Australian cities, the use of stormwater for aquifer recharge and supply augmentation is largely accepted and more positively perceived than recycled wastewater (Mankad et al., 2015).

Water acceptance studies deliver divergent conclusions with few overarching commonalities, but many local specific factors. The resulting insights from comparisons of acceptance studies cover a large breadth of issues. Often, review studies (e.g., Dolnicar et al., 2011; Duong and Saphores 2015; Hurlimann and Dolnicar 2016; Wester et al., 2016; Fielding et al., 2018) will stress factors including socio-demographic characteristics of respondents, reuse technologies and locations, contextual challenges facing water reuse (Table 1), (risk) perceptions and trust, socio-psychological factors (e.g., disgust), and socio-political environments (e.g., politics, role models, etc.). The key conceptual difficulty here is that these categories of acceptance factors/determinants relate to different aspects of the water acceptance phenomenon. Many studies do not define key concepts such as the acceptance by whom? (e.g, acceptance by “users/consumers”, “stakeholders”, the “reuse sector”, or the “public”) and of what? (i.e., which source, use or technology, and in which sites). Furthermore, the divergence of results is indicative of the temporality of water reuse acceptance: i.e., water reuse acceptance varies with the change in innumerable site-specific factors (e.g., adaptation to use, trust, policies, awareness, modernization, etc.). At the same time, the standalone approach of water reuse surveys is often inadequate for capturing the complexity of acceptance, as it gauges mere incidents or snapshots of supports, acceptance, or other momentary attitudes (e.g., favorable or skeptical).

As will be explained in the following sections, water reuse acceptance should be framed as an acceptability problem that is not merely related to individual or group attitudes, nor is it entirely a matter of public opinion. The demand for a more nuanced and contextual understanding of acceptability based on social norms and processes was also reiterated by other studies (e.g., Ching 2016; Crampton et al., 2016). Such a broad understanding of acceptance can lead to broader recommendations and can be used for structuring knowledge from acceptance case studies (Discussion). In a similar sense, Harris-Lovett et al. (2015) viewed potable water reuse from the broader perspective of whether a reuse technology is seen as legitimate or desirable in a certain social context. Beveridge et al. (2017) consider the whole water reuse issue as inherently social, with important spatial and political dimensions. Using a review of the relevant literature, this paper argues that the acceptability of water reuse projects requires a holistic understanding as a multi-layered social process of interactions between humans, technology and nature that takes place in norm-based and interlinked debates in both the public and private spheres.

The framework presented here to understand social acceptability (the willingness to accept) distinguishes four components (public perception, politicization, individual acceptance, and use adaptation), in which the debate about water reuse takes place and thus the view on water reuse is shaped (Figure 2). Policymakers can address each social acceptability component through various instruments, to be presented later in Mapping solutions across the social acceptability components. For a high acceptability of water reuse, the majority of debates on all components need to end with positive outcomes, since these components are largely interdependent. In each of the respective social acceptability components, one or more of the three issues or aspects of water reuse (water source, treatment technology and reuse purpose) figures prominently. As argued previously in A Synthesis of the Reuse Acceptance Enigma, water reuse experiences and acceptance vary significantly based on these three issues (source, technology and use). These issues are embedded in debates on other reuse challenges (In Company with Acceptance: Complementary Challenges of Large-Scale Water Reuse), which, in turn, can also affect the social acceptability of water reuse.

The social acceptability process of water reuse is divided into two main debates, the public debate and the private one. These debates are interrelated, while acceptance studies usually provide snapshots of sub-topics in one of these debates. These studies can be classified as placing more emphasis on either the private debate (Evidence highlighting the private debate dimension) or the public debate (Evidence highlighting the public debate dimension), but they often start from one acceptability component and ultimately recommend remedies beyond this particular component. This is due to the fact that improving water acceptance is rarely possible through a simple set of interventions (See Discussion).

The private acceptance debate of water reuse is influenced by considerations regarding the use purpose and treatment technology of the recycled water. This is repeatedly highlighted in bodies of literature using methods such as surveys, perceptions, or narratives and psychological tests (Evidence highlighting the private debate dimension). Individual acceptance depends on risk perceptions associated with certain reuse purposes such as drinking, cooking or irrigation. As mentioned previously, this is a highly individual process influenced by previous experiences, attitudes towards the environment, personal values or discussions with others (Bennett et al., 2010; Doria 2010; Ching 2016). Individual acceptance is susceptible to influences from political debates and public perception, but is also independent from these debates to a certain extent. For example, economic factors such as the cost of recycled water, incentives or subsidies for different reuse purposes can help to increase individual acceptance; e.g., (Molinos-Senante et al., 2013; Duong and Saphores 2015; Ravishankar et al., 2018; Sgroi et al., 2018). Similarly, use adaptation entails a private debate concerned with the technology used to recycle water. Consumers try to acquire information about the quality of delivered water and the associated risks (Binz et al., 2018). They form their opinions on the use safety and the required measures before the final use, e.g., filtration mechanisms or heating of water, depending on the source. Debates about the reliability of water treatment or other previously mentioned challenges of the safety of water reuse influence the determined use of recycled water by consumers. Ultimately, the ability to adapt to the use of recycled water is highly relevant for the individual acceptance, and often independent from other factors such as ideology and values.

Public perception is the most difficult, but arguably the most important, component of social acceptability. Indeed, under this component, all kinds of political, technical or scientific, religious and cultural debates take place in public and with the participation of various actors such as policymakers, scientists and experts as well as public and religious figures. The importance of this public debate is highlighted by several bodies of research on reuse acceptance, such as economic, institutional and social studies (See Evidence highlighting the public debate dimension). Ideas and norms compete in these debates to form an important public perception of water reuse. Here, the media is an important factor in this regard, while the debates are often less technical and rather broad; e.g., benefits vs. advantages of reuse, or reuse as desirable or alarming (Russell and Hampton 2006; Ching 2010; Lee and Tan 2016). The outcomes of public debates can be determined by a number of locally specific issues such as scarcity conditions, socio-political systems, role models and religious/cultural aspects (Po et al., 2003; Robinson et al., 2005; Hartley 2006; Doria 2010; Garcia-Cuerva et al., 2016; Hurlimann and Dolnicar 2016). During public debates on water reuse, politicization represents a deliberative process to highlight reuse as relevant for a society’s development, peace and order, relationship with nature, etc. At the same time, water reuse can become politicized in the wake of contamination incidents, project failures or constraints in the reuse system (Russell and Hampton 2006). However, in line with securitization theories (e.g., Allouche et al., 2011; Fischhendler 2015), politicization often takes place as a way to promote water reuse and prioritize action towards achieving it. Issues related to the water source such as water quality, source control, trust in supply authorities and effects of communities at the source are at the forefront of politicization debates (e.g., Fischhendler 2015; Beveridge et al., 2017). In cases of politicization incidents, these can significantly affect public perception.

Traditional perception studies (e.g., Robinson et al., 2005; Hartley 2006; Russell and Hampton 2006; Carr et al., 2011; Buyukkamaci and Alkan 2013; Aitken et al., 2014; European Commission 2015; Crampton et al., 2016; Garcia-Cuerva et al., 2016; Hurlimann and Dolnicar 2016; Baghapour et al., 2017) look at public responses to water reuse projects using perception and opinion surveys. This body of literature represents the most common approach in water acceptance research. The surveys de facto target the individual acceptance component of the social acceptability process. As highlighted previously in the review of similarities and divergences of experiences of acceptance of water reuse, (A Synthesis of the Reuse Acceptance Enigma), issues related to the particular use (i.e., Which source and technology is used for which use purpose?) dominate debates in acceptance surveys. Since individual acceptance lies at the center of the social acceptability process of water reuse, it is influenced by all of the other components. In this sense, acceptance surveys often link incidences of the acceptance or rejection of a certain water reuse issue to factors that might arise from other acceptability components.

In reality, traditional acceptance studies use individual acceptance or perceptions as a starting point of analysis. They then gauge a plethora of determinants related to the characteristics of individuals, debates in the public sphere, and contextual issues that represent the challenges related to water reuse (earlier described in Table 1). Some overviews of the determinants of acceptance and contextual challenges found in acceptance surveys are provided in Fielding et al. (2018), Dolnicar et al. (2011). Although some studies (e.g., Duong and Saphores 2015; Ravishankar et al., 2018; Smith et al., 2018) investigate “public” or “social” perceptions or acceptance, the focus is less on analyzing discourses or debates happening in the public sphere; rather, these mostly survey-based studies center on users’ acceptance and its determinants. Finally, since the focus of the traditional studies is on the conceptual constructs of perception, attitudes and acceptance incidents, the suggested remedies are mostly informational; i.e., stressing awareness, debates, education campaigns, etc.

Psychological and narrative studies (e.g., Hampton 2004; Menegaki et al., 2009; Ching 2010; Ching 2016; Leong 2016; Wester et al., 2016; Greenaway and Fielding 2020; Nemeroff et al., 2020) look at factors affecting individual attitudes towards water reuse. These factors include internalization processes of certain opinions, individual experiences, discourses, semantics, framing of water reuse information, etc. The methods deployed include surveys, observations or narratives and conceptualizations based on grounded theory. In the social acceptability process, the starting point for psychological studies is often the use adaptation component; e.g., disgust experiences (the yuck factor), emotions, or lived experiences. Often, psychological determinants such as disgust are presented as the most relevant determinants or predictors of acceptance (e.g., Duong and Saphores 2015; Wester et al., 2016). However, disgust is also seen as resulting from other factors. For example, education, prior knowledge, psychologically prepared information, labeling and public debates can mediate disgust experience (Ching 2010; Wester et al., 2016; Goodwin et al., 2017). In this sense, the recommendations of psychological or narrative-based studies often go beyond the component of the use adaptation.

Other studies in this body of literature relate emotions, attitudes and willingness to use to environmental values and personal profiles. For example, one approach in psychological studies is to link disgust with peoples’ sensitivity/aversion towards contagion/cleanness (Fielding et al., 2018). While these approaches are highly revealing about processes in the private acceptance debate of water reuse, some insights, e.g., on the “yuck discourse”, is of limited value for explaining how to change peoples’ responses towards water reuse (Russell and Lux 2009). Therefore, it is important to translate psychological insights into actionable implications. For example, psychological insights can help to improve the design of environmental nudging (Byerly et al., 2018), the targeting of awareness campaigns, the framing/labeling of water reuse strategies (McClaran et al., 2020), or interventions to facilitate the adaptation of households (Nemeroff et al., 2020).

Economic and institutional studies (e.g., Lloyd Owen 2016; Molinos-Senante et al., 2013; Menegaki et al., 2007; Fan et al., 2013; Garcia and Pargament 2015) reiterate the role of economics and contractual (rights-based) approaches in improving acceptance of water reuse. The basic premise here is understanding such acceptance as a regulation problem. This means that better rules and incentives can improve the outcomes of challenges directly affecting reuse acceptance, particularly those challenges of safety, distribution, participation, economics and governance. In this sense, the literature on these related challenges presented in Table 1 can also be seen as a part of this body of academic literature; e.g. framing water reuse as a function of better communication among agencies (Aldaco-Manner et al., 2019), or holistic circular economy strategies (Sgroi et al., 2018). Furthermore, improving regulation and the institutional set-up of water reuse can yield favorable outcomes in debates happening in all components of the acceptability process. However, the focus is rather on the public acceptance debate. Regulating resource allocations and (private) incentives for water reuse is a task centered in the overall governance or public policy context.

Closely related to the economic and institutional studies are social legitimacy and justice studies (e.g., Russell and Lux 2009; Harris-Lovett et al., 2015; Binz et al., 2016; Beveridge et al., 2017), which stress the complementary aspects of legitimate processes and decision-making, participation, consultations and transparency. The focus here is rather related to the public debate on reuse acceptance and whether the public perceives the system and technologies of water reuse as adequate, necessary, legitimate, transparent, or trustworthy. Often, studies in this body of literature use mixed methods and provide critical insights into classic approaches to understanding acceptance. For example, Russell and Lux (2009) criticized the premises that disgust and lack of information or awareness are deterministic for people’s responses. Instead, they propose a cultural (rather than psychological) approach in which people’s responses to reuse are seen as amendable through understanding local contexts and complexities and designing a participatory/deliberative planning structure for water reuse schemes. Another example is the framing of water reuse in California as a broad endeavor (beyond acceptance) to achieve the legitimacy of this new technology/innovation through institutional work and legitimacy strategies (Harris-Lovett et al., 2015; Binz et al., 2016).