Analysis on the Knowledge Evolution Path of Public Acceptance of Reclaimed Water Research

Abstract

Reclaimed water is an important component of available water resources, and public acceptance of reclaimed water is a key factor influencing the implementation of reclaimed water reuse projects. For this reason, it has received attention from different scholars in the international community. Based on the literature data on public acceptance of reclaimed water, this study analyzes the development status of research results and explores the knowledge evolution path with the help of bibliometric methods. Our results show that the field of research on public acceptance of reclaimed water began to grow rapidly after 1990, and identify influential countries, institutions, authors, and journals in the field. In addition, “water quality”, “public health”, and “irrigation” are themes that run throughout the research, and “sustainable development” and “potable reuse” are the emerging research hotspots. As research progresses, the scope of research on reclaimed water reuse and its influencing factors continues to expand, and reclaimed water management policies and standards continue to improve. In the future, in order to improve public acceptance, finding how to improve the public’s risk perception and trust in reclaimed water will become a central research focus.

1. Introduction

Water is a precondition for human existence and for the sustainability of the planet [1], and it is a necessary resource to secure for drinking water, to maintain sanitation and hygiene, and to sustain life and health. However, along with climate change and rapid population growth, water scarcity is a growing problem. According to the United Nations, global water consumption has increased sixfold over the past 100 years and is still growing steadily at a rate of about 1% per year [2]. It is estimated that by 2030, about half of the world’s population could have to deal with water scarcity [3], with more than 85% of the population in the Arab region living in water-scarce conditions [4]. An important solution to current and future water shortages is to increase the availability of unconventional water sources. Reclaimed water is widely valued as an alternative water source that is less expensive than desalination and water transfer projects, more stable than rainwater sources, and with the unique advantage of reducing environmental pollution [5].

Reclaimed water treatment technologies are able to treat reclaimed water to the desired water quality specifications, even to drinking water levels, depending on the different reuse applications. Sustainable Development Goal 6 of the United Nations’ 2030 Agenda for Sustainable Development clearly states that international cooperation and capacity building in wastewater treatment, recycling, and reuse technologies in developing countries will be continuously supported until 2030 [6], which is proof of the World Health Organization’s recognition of the safety of reclaimed water. However, reclaimed water remains controversial and is rejected as water from wastewater treatment [7]. Even among residents of arid regions, there is a lingering perception that reclaimed water is unclean [8]. In particular, the higher the degree of contact between reuse and the human body is, the stronger the public’s resistance and aversion [9], which ultimately leads to low reuse rates and the ineffective mitigation of water scarcity [10]. Therefore, different scholars have conducted a series of studies on the public acceptance of reclaimed water, focusing on the history of reclaimed water development, reuse cases, promotion experiences, and factors influencing public acceptance.

Research results obtained on the public acceptance of reclaimed water can provide references and suggestions for realistic policy development, so it is necessary to systematically review the relevant literature. Smith et al. (2018) systematically reviewed the literature on public responses to reclaimed water since the 21st century with the help of social science methods, focusing on describing the influencing factors, mechanisms of action, and response formulation [8]. Similarly, Nemeroff et al. (2020) focused on the psychological aspects of decision making, reviewing the rationale associated with increasing urban reclaimed water acceptance and proposing factors that influence adaptation insensitivity to complement existing research [11]. Furlong et al. (2019) summarized public attitudes towards drinking reclaimed water, the influencing factors, and strategies to promote public acceptance [12]. On the other hand, Fielding et al. (2019) summarized the reasons for the public acceptance of reclaimed water and the methods and experiences that successfully improved the public acceptance of reclaimed water mainly based on previous empirical studies [13]. Meanwhile, Mankad et al. (2011) identified key social and empirical drivers that may be associated with the acceptance of decentralized water systems through the empirical literature on the community acceptance and adoption of various alternative water systems [14]. In addition, Al-Saidi (2021) systematically discussed the challenges facing the public acceptance of reclaimed water in terms of three integrated factors: reclaimed water sources, treatment technologies, and end uses; and constructed an intellectual framework for the acceptance of reclaimed water reuse [15]. It was found that previous studies have reviewed the public acceptance of reclaimed water from different focus points, but there is still a lack of review studies that use bibliometric methods to comprehensively analyze the main lines of knowledge development in the field of public acceptance of reclaimed water.

Therefore, this study takes the literature related to the public acceptance of reclaimed water as its research object, quantifies current research results from the temporal aspect, and conducts a general statistical analysis of their number of publications, citations, authors’ H-index, journal impact factor (JIF) and other information at the macro level so as to clarify the development status of the public acceptance of reclaimed water. We explore the trajectory of knowledge development from the origin and evolution of the field, determine the research focus and hotspots in different periods with the help of keyword co-occurrence analysis, identify the core literature in this field through main path analysis, and then establish the knowledge theme structure. Finally, we obtain the evolution path of research in this field, providing a useful reference thereby helping scholars to quickly understand the frontier hotspots in this research field.

2. Research Data and Methods

2.1. Data Source and Data Acquisition

Since awareness and acceptance are usually explored in research with the help of factors such as “opinion”, “attitude”, “trust”, and “willingness to pay” [16], in this study we decided to use “perception”, “attitude”, “belief”, “acceptance”, “resist”, “disgust”, “support”, “oppose”, “yuck factor”, “agreement”, “participate”, “willingness to pay”, and other keywords as the search terms for the concept of “acceptance” after a preliminary search to ensure the integrity of the data. The public commonly plays the role of residents and consumers in the process of reclaimed water reuse, so the keywords of “people”, “public”, “consumer”, “resident”, and “citizen” were used as the search terms for the concept of “public”. In this study, the Web of Science (WoS) core sets of SCI, SSCI, A&HCI, ESCI, CPCI-S, and CPCI-SSH were used as the sources to obtain and download literature data, and the following searches were conducted.

(TS = (“reclaimed water” OR “recycl* water” OR “reus* water” OR “water reuse” OR “wastewater reuse” OR “intermediate water” OR “middle water” OR “reclaimed wastewater” OR “wastewater reclamation” OR “sewage reclamation” OR “reclamation of sewage” OR “sewage reutilization” OR “sewage recycling” OR “waste water recycling”) AND TS = (percept* OR attitude* OR belief OR acceptance OR resist* OR disgust* OR support* OR oppos* OR “yuck factor*” OR agreement* OR participat* OR “willingness to pay” OR behavior*) AND TS = (people OR public OR consumer* OR resident* OR citizen*)) AND LA = (English)

Indexes = SCI, SSCI, A&HCI, ESCI, CPCI-S, CPCI-SSH

PY = ALL YEARSDT = All document types

Search Results: 1108 records, Date last updated: 20 February 2022 (GMT + 8)

To ensure the topic relevance of the retrieved articles, the search scope of this paper included titles, abstracts, and keywords, and a total of 1108 documents were retrieved. After checking, it was found that the retrieved literature data contained 1 duplicate record and 372 irrelevant records, and 735 valid documents were finally obtained through manual screening.

2.2. Research Methodology

Bibliometrics is the analysis of publications and their related metadata (such as abstracts, keywords, and citations), mainly through statistical data, to describe publication trends and highlight relationships between publications [17], in order to make analyses more objective and reliable [18]. In this study, the evaluative bibliometric method was used to describe the information characteristics of publications, identifying authors, countries, institutions, journals, etc., that have made significant contributions to the field. Co-word analysis from relational bibliometrics was used to identify research topics in the field, and main path analysis was used to clarify the relationships between citations in the research literature and to determine the trajectory of knowledge development in the discipline. The above analyses were implemented with the help of the Histcite, VOSviewer and Pajek software. The Histcite software not only provides a data basis for citation analysis, but also allows one to visualize bibliographic information, which helps the researcher to quickly target important information in the research field. VOSviewer is a software tool used for building and visualizing networks with a special emphasis on the graphical representation of bibliometric graphs. The Pajek software can identify critical paths in the field and then track key research results, sort out the main development lines, and reveal the evolution of research themes [19].

The specific research idea of this paper is shown in Figure 1. Based on the literature data, the development trends and research status within the field of public acceptance of reclaimed water were analyzed from the temporal aspect using an evaluative bibliometric approach, and the trajectory of thematic evolution and knowledge development within the field of public acceptance of reclaimed water research was analyzed from the evolution of the field using a relational bibliometric approach.

3. Results

3.1. General Statistical Data Analysis

With the help of the HistCite software, the number of publications, citations, authors, journals, and other relevant information in the field of public acceptance of reclaimed water research were identified. Additionally, the statistics were visualized to obtain Figure 2, which reflects the development of the field from 1969 to 2022.

Figure 2a,b display the number of publications and citations, respectively, in the field of public acceptance of reclaimed water in different years, clearly showing the increasing research into public acceptance of reclaimed water in academia. First, the number of publications has gone through three successive phases. Between 1969 and 1990, the number of publications per year changed gently, with the number of articles at 0-2. However, from 1991 to 2000, the number of publications per year was unstable, especially in 1991 when there was a surge, with the number of publications increasing to 18 from 0 in the previous year. Between 2001 and 2022, the number of articles per year increased, reaching the highest annual number of 75 articles in 2021. Secondly, the number of citations associated with the articles showed a similar variation to the number of publications in the previous period and reached a peak of 288 in 2009, but after 2016 the number of citations fluctuated more. Notably, the most cited article, “Desalinated versus recycled water: public perceptions and profiles of the acceptability of water” by Sara Dolnicar and Andrea I. Schäfer, appeared in 2009 (LCS = 97). There is an accelerating trend in the number of publications and citations of public acceptance of recycled water over time.

According to Figure 2c, scholars in the United States have made the most prominent contribution to research on the public acceptance of reclaimed water, with 220 publications. Australia comes second with 131 publications, and China ranks third with 63 publications. The United States and Australia both have a long history and much experience of recycled water reuse and are clearly ahead of other countries in terms of public acceptance. China, on the other hand, has also been conducting rapidly increasing studies on the promotion and application of reclaimed water due to the growing problem of water scarcity. Of the top thirteen institutions in terms of the number of publications, seven are from the United States, four are from Australia, and one each are from Singapore and China (Figure 2d). The top three institutions with the highest number of publications are Xi’an University of Architecture and Technology in China, the University of Melbourne in Australia, and the University of Arizona in the United States. The number of publications from Xi’an University of Architecture and Technology accounted for one third of the total studies on this topic in China, representing an outstanding contribution in this field. Figure 2e shows the top five most influential scholars: Dolnicar S and Hurlimann A from Australia, Fu HL and Liu XJ from China, and Ormerod KJ from the U.S. Among these, the number of individual citations and the H-index of Dolnicar S and Hurlimann A are the highest, reflecting their authority and influence in the field; they have collaborated on 11 articles.

Figure 2f represents the top 11 journals in research on the public acceptance of recycled water. It can be seen that Water Science and Technology, with 59 articles, is the journal with the highest number of publications. Additionally, the journal Water, ranking second with 41 articles, is an influential journal in the field. In addition, Water Research, Desalination, and Journal of Environmental Management all have more than 20 articles, with more than 10 citations per article. Overall, most of these journals have high impact factors, indicating that the articles published in these journals are recognized by scholars in this field.

3.2. Research Topics and Hotspot Analysis

According to the above analysis, there were very few studies on the public acceptance of reclaimed water before 1990, so the literature data from 1991 to the present were selected as the data source for a keyword co-occurrence analysis. At the same time, we divided the total research time into three periods based on the trend of the number of publications in this field: from 1991 to 2000 (exploration stage), from 2001 to 2010 (growth stage), and from 2011 to 2022 (mature stage). Based on the cleaning of keyword data, the co-occurrence analysis function of the VOSviewer software was used to construct the co-occurrence keyword networks for each stage, as shown in Figure 3, Figure 4 and Figure 5. The size of the key nodes in the graphs represents the frequency of keyword occurrences, the node color represents the average year of keyword occurrences, and the yellow nodes represent the current emerging research topics.

3.2.1. The Period of 1991–2000 (the Exploratory Stage)

Figure 3 presents the keyword co-occurrence networks and clusters in the field of public acceptance of reclaimed water during the period 1991–2000. We can see that the research is divided into four clusters, and the research hot topics include “water quality”, “water supply”, “drought”, “irrigation”, etc. From cluster 1, we can see that reclaimed water is used in daily life and its quality is of great concern [20]. The most important thing is to protect public health and environmental safety in the use of reclaimed water. Therefore, there is an urgent need for countries around the world to formalize their wastewater treatment and reuse practices by standardizing corresponding technical specifications for reclaimed water treatment and reclaimed water reuse index requirements. Additionally, authors from different countries agree that reclaimed water has the ability to fulfill the expected reuse demands [21]—that is, the index requirements will vary depending on the reclaimed water reuse purposes. For example, Japan’s reclaimed water reuse guidelines specify the requirements for microbial content, turbidity, and color of recycled water [22], while for the quality of reclaimed water intended for decorative purposes, two types of standards were proposed: recreational reuse with close contact and ornamental reuse for scenery [23]. The keywords in Cluster 2 show that for reclaimed water intended for irrigation purposes, the Superior Council of Public Hygiene of France has developed guidelines for reclaimed water use in the area of agricultural irrigation. In order to ensure public health protection and maintain the beauty of the landscape, Mas Nou Golf Course in Spain formulated standards for reclaimed water used for golf course irrigation [24]. In addition, for the case of irrigation, the contents of nitrogen, phosphorus, disinfectant components, and nutrients were explored in detail in the later stages of this study.

Secondly, with the accelerating pace of industrialization and urbanization worldwide, the problem of water scarcity in several countries has become apparent. Research content related to Cluster 3 shows that the reuse of reclaimed water can help meet the additional demands on water resources in a short period of time, ensuring both the reuse of water resources and the effective treatment of wastewater. Many countries in the Near East have developed plans for the large-scale use of such unconventional water sources [25], and wastewater recycling and reuse should become integral parts of water management strategies in many arid and semi-arid countries [26]. Meanwhile, some studies have suggested that communities need to install reclaimed water distribution systems in order to use reclaimed water for miscellaneous urban and industrial purposes such as landscape irrigation, toilet flushing, and car washing. Cluster 4 indicates that although government departments have realized the great potential of reclaimed water, the public at this time lacks sufficient understanding of the issues of water conservation and water reuse and has a strong bias against the reuse of reclaimed water. At this stage, the public is often limited to receiving reclaimed water for landscape greening and the irrigation of animal feed crops [27], and research on the reuse of reclaimed water for drinking purposes is only at the level of exploring its feasibility [5]. Studies have found that education can be used to increase the public’s understanding of the current drought situation and the benefits of reclaimed water, thereby increasing the public acceptance of reclaimed water.

3.2.2. The Period of 2001–2010 (the Growth Stage)

Figure 4 presents the mapping and clustering of knowledge topics in the field of public acceptance of reclaimed water during the years 2001 to 2010. It was found that the research on this stage mainly centered around five aspects, including “water management”, “public health”, “irrigation”, and “desalination”. Cluster 1 shows that water management was still the focus of research in this period, and different countries developed different approaches to reclaimed water management based on their understanding of the health risks involved and their economic and environmental carrying capacity. For example, China adopted the Sustainable Urban Sewage System (SUSS) as the basis for its urban water resources recycling [28]. Meanwhile, Germany established a framework for best management practices and increased public awareness of reclaimed water as two important aspects of strategic planning for the reuse of reclaimed water [29]. Some Mediterranean countries implemented the EMWater project to find solutions for improving the security of their water supplies by raising public awareness of the issue and implementing new techniques for wastewater treatment and reuse [30]. France developed a comprehensive technical and economic model as a tool for water resource planning and management, considering wastewater recycling for crop irrigation as the most cost-effective solution to address water scarcity and protect sensitive environments [31]. At the same time, the irrigation of food crops with reclaimed water had become more common, but there remained multiple issues related to food production, life and health, environmental risks and socio-economics [32]. Therefore, agricultural irrigation also received a lot of attention in this period.

In Cluster 2 it was shown that the United States used decentralized wastewater management (DWM) systems to protect public health and environmental safety [33], but due to the lack of technical and scientific knowledge, only 2% of reclaimed water was eventually used for the irrigation of stadiums and public landscapes [34]. It can be found that public health and environmental safety issues were not only important reasons for the low use rate of reclaimed water, but also some of the main reasons for the low level of public trust and willingness to accept it. Therefore, in order to reduce the hazards and impacts related to the use of reclaimed water, relevant authorities formulated a large number of regulations for water quality. It can be summarized that although there were internal national standards for the reuse of reclaimed water, the reuse of recycled water and public acceptance were still severely constrained by the lack of common regulations at the international level for a long period of time, with different standards with contradictory requirements existing simultaneously in the same country [35]. On the other hand, water supply companies, wastewater treatment plants, and other authorities improved the accessibility and visibility of water quality information through innovative technologies for testing reclaimed water quality in order to report reclaimed water reuse incidents faster and more accurately, and to improve public health risk management. In addition, studies focused on the importance of economic factors and suggested that for the integration of reclaimed water reuse into global water management, socio-economic barriers must be overcome, cost effectiveness must be achieved, and public health requirements must be met [36].

Cluster 3 showed that at this stage, reclaimed water was used for landscape irrigation and other non-potable urban applications to some extent, providing an opportunity for the expanded application of reclaimed water. In terms of technology and planning, an integrated techno-economic model was developed for urban water management, and multiple options for reclaimed water reuse for miscellaneous urban applications were evaluated to find the most cost effective option. In terms of project implementation, new water recycling systems were established in public areas, commercial areas, and residential areas for water recycling and reclaimed water distribution for the purposes of toilet flushing, green irrigation, road sweeping, firefighting, and other non-potable applications. Studies investigated the attitudes of urban residents toward reclaimed water and found that most residents supported medium-contact reuse options, including sidewalk landscaping, firefighting, etc. A few residents were able to accept higher-contact-level reuse options [37]. The keys to the success of water reuse projects for landscape irrigation and other unban reuse, however, lay in preserving public health; overcoming restrictions and opposition; and paying special attention to the reliability of operation, economic feasibility, and the level of stakeholder involvement [38]. In Cluster 4, desalinated water and reclaimed water entered the study as two popular alternative water sources to protect existing water resources and address the problem of water scarcity. By comparing reclaimed water with water sourced from seawater desalination, it was found that reclaimed water was a cost-effective solution [39], and public willingness to accept it was often the major hurdle facing the implementation of these solutions [40]. From Cluster 5, it can be seen that in the treatment of reclaimed water, the pathogen content needed to be to reduced according to relevant standards in order to achieve sustainable and safe reclaimed water reuse, and the risk assessments on the reuse of reclaimed water mainly aimed to analyze and calculate the potential risks posed to human health from microbiological, chemical, and biological factors [41]. At the same time, case summaries and research studies revealed that the factors influencing the public acceptance of reclaimed water included not only psychosocial factors such as risk perception, trust, environmental awareness, and the acceptance of new technologies, but also demographic characteristics such as gender, age, education level, and financial status.

3.2.3. The Period of 2011–2022 (the Mature Stage)

Figure 5 presents keyword co-occurrence networks and clusters in the field of public acceptance of reclaimed water from 2011 to 2022, revealing that the focus of attention during this period covered five areas: “sustainable development”, “water management”, “irrigation”, “potable reuse”, and “public health”. From Cluster 1, it can be seen that ”sustainable development” was the most popular topic in this current stage, moving from a marginal topic in the previous stage. Additionally, water resources played an important role in the sustainability of ecology, economy, and public health. Research showed that water has an important role to play in the circular economy and public health, and the effects of climate change on water were shown to influence all aspects of ecology and socio-economics [42]. Therefore, ensuring that water resources meet multiple needs has become a challenge for global sustainable development [43] and one of the main tasks of the international community. For example, studies showed that Bangkok used Dispersed Wastewater Management (DWWM) to promote Sustainable Urban Development (SUD) [44], while Jordan promoted the use of decentralized grey water treatment systems in small rural communities to achieve a more sustainable water supply [45]. Technically, reclaimed water is the most cost-effective and environmentally sustainable solution [46] to this problem, and people are aware of the need to use reclaimed water to address the issue of water scarcity, but it is difficult to overcome the psychological fear of accepting reclaimed water [47].

According to Cluster 2 and Cluster 3, agricultural irrigation and potable reuse were the two most popular reuse applications in the most recent stage. According to the United Nations 2021, agricultural water accounted for 69% of the use of global freshwater resources, and the use of reclaimed water for agricultural irrigation has had great success in alleviating the problem of water shortages globally. Although the use of reclaimed water for agricultural irrigation is not strange, the potential of reclaimed water for agricultural water has not been fully exploited and public attitudes largely remain negative [48]. To solve this problem, in addition to promoting public acceptance by improving uniform laws and standardizing guidelines, the long-term testing of soil indicators and comprehensive risk assessments are needed. Additionally, promoting public participation in water quality monitoring was also proposed as a means by which to increase public trust [49]. On the other hand, potable reuse, as a special reuse purpose, has become a new research focus. After a lot of research, it has been found that there is a lack of practical experience in the potable reuse of reclaimed water. Not only can the drinking risk not be accurately predicted, but the related policies and regulations also need to be developed further. This has led to a lack of public trust in the relevant authorities and a low willingness to accept drinking recycled water [50]. Even in Australia and the United States [51], which are world leaders in the field of reclaimed water reuse, the reuse of reclaimed water for drinking purposes is frequently hindered.

In addition, Cluster 4 shows that in recent years, climate change and population growth have led to severe droughts in several countries, as represented by Australia. In order to address the issue of water demand and alleviate groundwater over-exploitation, multiple solutions including seawater desalination, rainwater collection and reclaimed water reuse have been proposed. In addition, investment decisions were made with the help of the contingent valuation, which weighs multiple criteria such as the security of supply, cost, energy consumption, ecological impact, public health impacts, and social acceptability, and selects the best combination of alternative water sources and different drivers. According to the public acceptance survey, the majority of the public have an aversion to reclaimed water, but view desalinated water as mineral water or as “simple water” [52] and are more willing to accept desalinated water as an alternative source. It is clear from Cluster 5 that rapid urban development provides a favorable opportunity to expand the use of reclaimed water in urban areas, and that the reuse of reclaimed water can reduce a city’s dependence on groundwater. A comparison of reclaimed water with conventional water sources revealed that reclaimed water used less energy in its production and supply and produced less carbon dioxide [53]. While city residents are aware of the economic and environmental benefits of reclaimed water [54], the rate of reuse of reclaimed water is not promising. As a result, studies summarizing the success of the reuse of reclaimed water for municipal green area irrigation, cleaning, industrial, commercial, and fire protection purposes found that the key aspects needed to increase public trust in reclaimed water were the strong commitment of elected officers to this goal and a large base of industrial users [55]. This proves once again that public risk perception and social trust are the key influencing factors of reclaimed water, driving global actions to identify more accurate risk assessment methods and more reliable recycled water treatment technologies. Based on the average year of the keywords, it can be predicted that the future research will follow the trend of sustainable development and pay more attention to the circular economic analysis of reclaimed water. Moreover, risk perception, public trust, and public acceptance of the potable reuse will also become the focus of future research.

3.3. Main Path Analysis

Based on the citation network of research results in HistCite, this study used the Search Path Count (SPC) algorithm in the Pajek software to calculate the traversal weights of the specified citation relationships. Additionally, the study extracted the key-route main path in the public acceptance of reclaimed water, as shown in

Table 1. The main path and key articles note information.

Main Path	Author(s)	Title	Journal
	Bruvold H. William	Public opinion on water reuse options [56]	Water Pollution Control Federation
	Troy W. Hartley	Public perception and participation in water reuse [57]	Desalination
	Sara Dolnicar, Andrea I. Schäfer	Desalinated versus recycled water: public perceptions and profiles of the accepters [58]	Journal of Environmental Management
	Sara Dolnicar, Anna Hurlimann	Drinking water from alternative water sources: differences in beliefs, social norms and factors of perceived behavioural control across eight Australian locations [59]	Water science and technology
	Sara Dolnicar, Anna Hurlimann, Bettina Grün	What affects public acceptance of recycled and desalinated water? [60]	Water Research
	Victoria L. Ross, Kelly S. Fielding,Winnifred R. Louis	Social trust, risk perceptions and public acceptance of recycled water: testing a social-psychological model [61]	Journal of Environmental Management
	Kelly S. Fielding, Anne H. Roiko	Providing information promotes greater public support for potable recycled water [62]	Water Research
	Anna Hurlimann, Sara Dolnicar	Public acceptance and perceptions of alternative water sources: a comparative study in nine locations [63]	International Journal of Water Resources Development
	H.M. Smith, S. Brouwer, P. Jeffrey, J. Frijns	Public responses to water reuse—understanding the evidence [8]	Journal of Environmental Management
	Kelly S. Fielding, Sara Dolnicar, Schultz Tracy	Public acceptance of recycled water [13]	International Journal of Water Resources Development
	Wester Julia, Broad Kenneth	Direct potable water recycling in Texas: case studies and policy implications [64]	Journal of Environmental Policy & Planning

. The table displays the detailed information of eleven key literature nodes in the main paths, including the nodes of different colors representing the source points, intermediate points, and sink points. The arrows in between nodes represent the citing–cited relationships between articles.

The first core research in the main path is a study on public perceptions of reclaimed water reuse conducted by American scholar Bruvold William H. in 1988, when research began to focus on the feelings and perceptions of the public, the ultimate decision maker and largest user of reclaimed water, regarding reclaimed water [56]. In the 21st century, Troy W. Hartley (2006) explored the importance of public perceptions and participation in reclaimed water through a unique research perspective, using case studies, stakeholder workshops, and peer reviews by experts in the field. The author’s final conclusion was that enhancing public awareness of recycled water, establishing public and governmental department trust mechanisms, and improving the transparency around relevant water quality information have positive effects on the promotion of recycled water reuse projects [57].

The following three articles are all studies on the public reuse of reclaimed and desalinated water conducted by Australian scholar Sara Dolnicar as the first author. Additionally, one-half of the articles appearing in the main path are the work of Sara Dolnicar, again confirming her outstanding contribution to the field. The first article was published in 2009, and in it the authors Sara Dolnicar and Andrea I. Schäfer compare and analyze the public cognition and acceptance of alternative water sources for the first time. It was found that among the two alternative water sources, desalinated water had a higher acceptance intention for use involving human contact, while reclaimed water had a higher level of acceptance for other uses that did not require contact with the human body. In this article, the authors also proposed that people with experience of droughts and who are highly informed about water resources are more likely to accept the use of alternative water sources [58]. In the same year, Sara Dolnicar and Anna Hurlimann investigated the public attitudes toward desalinated and reclaimed water as drinking water sources. Through interviews with residents in different drought-affected areas, it was found that social norms were the most effective factors in preventing the public from drinking alternative water, while the information disclosed by the authoritative department had the most influence on encouraging the public to drink alternative water [59]. Sara Dolnicar and Anna Hurlimann et al. collaborated again in 2011 on influential research showing that the conceptual perception of alternative water sources is a key driver of decision making, and further demonstrating that the awareness of water shortage and experience with water reuse have a positive impact on the public acceptance of alternative water [60]. Notably, this research was the first to include both socio-demographic and psychographic characteristics in its hypotheses.

As research continues to advance, the factors influencing the public acceptance of reclaimed water have gradually been determined. Victoria L. Ross and Kelly S. Fielding et al. (2014) developed a psychosocial model of the trust in, risk perception of, and acceptance of reclaimed water. The level of public trust was found to be influenced by the degree of information sharing and reliability between the water authority and residents in a given area, and it was found that the higher the level of public trust was, the lower the perception of risk was [61]. In the same year, Kelly S. Fielding also compared the effects of information on public perceptions, emotions, and behavioral responses to reclaimed water reuse by controlling for the level of information disclosure, demonstrating that information disclosure increased comfort with drinking recycled water and that the public showed more support and lower risk perceptions [62]. In 2016, Anna Hurlimann and Sara Dolnicar collaborated for a third time to compare the public acceptance of three alternative water sources—reclaimed water, desalinated water, and rainwater—for different reuse purposes in nine international locations. Reclaimed water was found to be more acceptable for urban green irrigation and toilet flushing, with desalinated water and rainwater being preferred for all other purposes; it was also reaffirmed that people in water-scarce environments or with use experience of reclaimed water were more receptive to the use of reclaimed water [63].

The next two papers were reviews which systematically sorted and summarized previous studies. H.M. Smith et al. (2018) reviewed the research on the public response to reclaimed water since the beginning of the 21st century, focusing on the factors influencing the public reaction to reclaimed water and exploring the influence of trust, risk perception, and emotional factors [8]. Kelly S. Fielding et al. (2019), by summarizing the literature and project cases related to the public acceptance of reclaimed water, found a positive correlation between the degree of information disclosure and the public acceptance of reclaimed water. Additionally, the establishment of information sharing and trust mechanisms among stakeholders of reclaimed water reuse projects can help increase people’s willingness to reuse [13]. A more recent study (Julia et al., 2021) explored the linkages between regulatory, structural, environmental, political, and communication factors related to public attitudes based on the case and policy implications of cities implementing direct potable water recovery (DPR) policies in Texas, USA. Additionally, this research highlighted that externalized manifestations of aversion and risk perception are often public attitudes toward reclaimed water [64].

4. Discussion

As previously mentioned, the public’s acceptance of reclaimed water has attracted more and more research attention. On the one hand, the number of publications in this field is increasing significantly. On the other hand, the reclaimed water policies of various countries are gradually improving, and the voice of the international community advocating for unified standards is gradually increasing in volume. The countries with the largest number of publications are the United States, Australia, and China. As previous studies have shown, the United States and Australia have conducted such studies over a large time span and have rich experience in this field. As a developing country, China has taken the lead in focusing on the potential factors influencing the public acceptance of reclaimed water. Therefore, authors and institutions that have made outstanding contributions in this field frequently appear in these three countries. Secondly, the scope of this research continues to expand because the reuse of reclaimed water has expanded from agricultural irrigation and aquaculture applications to industrial water, miscellaneous municipal use, household cleaning, and finally to drinking, which has the closest contact with the human body. Moreover, the research content is deepening, because the research on the factors influencing the public acceptance of reclaimed water has deepened from focusing on superficial factors (such as personal cognition and drought experience) to psychosocial factors (such as risk perception, trust, environmental awareness, and information disclosure) and discussing the relationships between mechanisms of each influencing factor.

Meanwhile, the results predicted in the co-word analysis and the new studies conducted in the main path suggest that the question of how to improve the public’s willingness to drink reclaimed water will become the focus of future research, as will the influencing factors including risk perception, social trust, and their internal relations. It is worth noting that potable reuse of reclaimed water is highly controversial. In order to help potable reuse enter the stage of public acceptance and thus enable reclaimed water to truly enter the daily life of the public, future research formulating corresponding preventive measures for the potential risks of different reuse applications is needed. This will help to increase public trust in the authorities, reduce risk perceptions, and thus improve the public’s acceptance of reclaimed water.

5. Conclusions

Reclaimed water has received widespread attention from the international community because of its advantages in alleviating water scarcity and reducing water pollution. However, it has also been treated negatively by the public because of the unknown risks that it may pose to ecological, economic and social development. Public acceptance is the key factor in the success of the reuse of reclaimed water, so it has been widely studied by scholars in various countries. With the help of bibliometric methods, this study uses the literature in the field of public acceptance of reclaimed water as the basis for research, analyzes the development status through general statistical data, and identifies the research topics and knowledge development trajectories at each stage with the help of co-word analysis and main path analysis. The main research conclusions are as follows.

In terms of general statistical analysis: From the perspective of time distribution, during the period from 1969 to 1990, the number of publications related to the public acceptance of reclaimed water did not exceed two per year, and this field developed significantly after the surge in 1991; in particular, the quantity of publications greatly increased from 2001 onwards. From the perspective of spatial distribution, the United States was the country with the highest number of publications, with a total of 220 articles. Xi’an University of Architecture and Technology was the institution with the most publications concerning the public acceptance of reclaimed water, and its number of papers published accounted for 1/3 of the total research on this topic in China. The most influential author was Dolnicar S, a scholar from Australia, who ranked first in the number of publications, the number of single citations, and the H-index. Additionally, the journal with the largest number of publications was Water Science and Technology, while the journal with the highest impact factor was Desalination.

In terms of evolutionary path research: Through the co-word analysis, it was found that reclaimed water quality and public health were the key concerns in each stage, while the reclaimed water management methods and policy guidelines of countries around the world were constantly being enriched and improved upon. Secondly, research on the use of reclaimed water for irrigation purposes was conducted throughout the entire period, and the expansion of its use for agricultural irrigation and landscape irrigation could effectively solve the problems of large agricultural water consumption and the shortage of urban water resources. Finally, new research hotspots such as sustainable development, potable water, and circular economy emerged in the later stages of research. According to the main path analysis, after Bruvold William H. studied the public opinions regarding reclaimed water in 1988, scholars in various countries have identified the influential factors and water use preferences concerning the public acceptance of reclaimed water; this was achieved through the research perspectives of different reuse purposes, different driving strategies, and the ecological and economic benefits generated by the use of different alternative water sources. Additionally, several studies have put forward corresponding policy recommendations and guidance. Moreover, in recent years, the field has shown a high level of research enthusiasm about the factors influencing public acceptance of reclaimed water for drinking and the role of the relationship between them. In addition, research in the field of public acceptance of reclaimed water will continue to promote the potable use of reclaimed water and urban reclaimed water projects in the coming period, and will seek solutions to reduce public risk perception and improve social trust in it so as to achieve the ultimate goal of increasing public acceptance.

Finally, there are some limitations in this study. Firstly, this study only used the Web of Science Core Collection as the literature data source and did not include important literature that might be included in other databases in its analysis. Therefore, in future research, the data sources could be expanded to ensure the integrity and accuracy of the study. Secondly, the main path analysis only focused on a small number of core studies, with most of the work being filtered out, resulting in their content not being reflected. In the future, other research methods should be used to find key literature information that may have been missed here.