Governance Arrangements for Water Reuse: Assessing Emerging Trends for Inter-Municipal Cooperation through a Literature Review

Abstract

The transition towards a Water Circular Economy (WCE), in the sense of water reuse, demands cooperative governance and territorial rescaling to overcome fragmentations in sectors and water policies. While the transition is challenging for local governments and crosses economic sectors and spatial scales, Inter-Municipal Cooperation IMC is gaining popularity due to its ability to contribute additional human, financial, and technological resources. However, cooperative governance arrangements require studying its benefits and impacts in its context. This study explores how IMC is being considered as a governance arrangement for the transitions towards WCE by conducting a review of the literature. The findings indicate that IMC appears as a promising government arrangement for WCE because it incorporates several significant potentials, such as facilitating the conciliation of interests between agencies, stakeholder engagement, and effective land use for water management. The literature reflects that the success of IMC for the adoption of WCE requires the simultaneous consideration of a set of governance practices, the assurance of cost efficiency and financial balance, and the assessment of social and environmental consequences. Nevertheless, these dimensions are not equally addressed by the literature. While governance and efficiency are often referred to, the assessment of IMC experiences in the context of WCE is still poorly explored, deserving further research.

1. Introduction

Water Circular Economy (WCE) has emerged to address the shortcomings of past water resource developments and current water scarcity [1]. The transition to WCE is expected to generate valuable synergies through the adoption of water reuse as an alternative water supply [2]. WCE may involve reusing wastewater while reducing contamination of water bodies and pressures from abstraction [3]. Reusing water, however, may cause a complex set of risks for the environment and human health, requiring a wide range of new policies and regulations [4]. To face these risks, governance arrangements must be well designed to prevent risks [5] and to foster new monitoring requirements and allocation challenges [6]. Governance for WCE comprises robust inter-linkage of various issues, such as sector policies and regulations, improved monitoring schemes, financing and pricing, stakeholder collaboration, and public participation. It also involves many challenges, such as heterogeneous actors, fragmented knowledge and skills, institutional diversities, and overall coordination [7,8]. Considering that water bodies and related concerns cross administrative borders [9], institutional and territorial fragmentations may threaten policy coherence across sectors [10]. By enhancing and developing water consumption and supply and governance approaches in response to growing demands, the transition to WCE transcends economic sectors or spatial scales and challenges the currently fragmented local government approaches [11]. Inter-Municipal Cooperation (IMC) is one type of strategy adopted, especially in Europe, to address many of these challenges, as it may offer economies of scale, territorial size, and policy coordination through cooperation between local authorities [12].

The implementation of WCE may take place under various governance arrangements. With IMC, governance may be facilitated with the improved capacity of engaging local stakeholders and establishing a transboundary platform for sharing goals, visions, knowledge, and experiences [13,14]. Moreover, it facilitates cooperation under varied spatial and political contexts with different institutional, infrastructural, and socio-economic features [15]. IMC is a local governance arrangement aiming at bringing together more human, financial, and technical resources [16]. IMC is ‘all arrangements where local governments cooperate with each other, with other public authorities or with private institutions’ [17] (pp. 123). IMC emerged to cope with territorial boundary obstacles or to achieve joint objectives, governance or institutional structure, or cost and economic efficiency [18,19,20]. It provides a platform for city staff to share experiences, exchange information about regulatory requirements, and identify collaborative opportunities [21]. Even though the concept of IMC and its benefits and limits have been widely explored as a governance solution, little is known about the appropriateness and suitability of IMC arrangements to incorporate WCE. However, IMC is not a panacea, and the cooperative governance model raises the need to study its concerns and to check its benefits and impacts [11,21,22,23].

This study aims to understand how the literature addresses the appropriateness and suitability of IMC arrangements for a transition to WCE. For this purpose, it undertakes a review of the literature to explore major knowledge and gaps referred to by existing studies and recommendations for further research. This study uses three databases, a broad one with a selection of scientific articles on IMC and two others with articles crossing IMC and water and IMC and Circular Economy (CE). These aim to identify emerging knowledge about IMC as a government arrangement for WCE. This review of the literature firstly refers to the origin and the approaches of IMC, followed by focused reviews of articles crossing IMC to “water” and to “circular economy”. This study is guided by the following questions: How are IMC concerns associated with WCE? Is IMC considered a suitable governance arrangement for the adoption of WCE, and what are the considerations and requirements for IMC for the WCE adoption?

There are many studies reviewing the literature for different purposes, including IMC [24,25,26], IMC and water [18], and IMC and CE [27]. Nonetheless, this study brings a novelty as it provides evidence-based findings about how the literature is referring to IMC as a “suitable” governance arrangement for implementing WCE, which has not been scrutinised before.

This article is structured into four sections. Section 2 introduces the main methodological steps adopted to conduct the review of the literature and the features of the databases. Section 3 presents the main findings according to the different databases and topics. Section 4 discusses the results considering the features of the methodology and the database and concludes with final notes and recommendations for further research.

2. Materials and Methods

The literature review has been structured into two major steps. The first was dedicated to creating the databases of scientific articles for the study. Three databases were created, one with a selection of articles on IMC, another with articles crossing IMC and water, and another with articles crossing IMC and CE. For the database on IMC, the query retrieved 163 articles. Of these, 30 articles were selected using the 15 most cited articles to ensure coverage of the topic’s essential elements and 15 of the most recent studies to understand the topic’s evolution of knowledge. For the database on IMC and water, 29 articles were found and analysed. For the database on IMC and CE, 19 articles were found and analysed.

Table 1. The databases and search criteria of the literature review.

Databases	Query Used for the Search	Platforms	Retrieved Articles	Selected Articles for Analysis
IMC	inter-municipal AND cooperation OR collaboration OR intermunicipal AND cooperation OR collaboration OR inter-local AND cooperation OR collaboration OR interlocal AND collaboration OR cooperation	Scopus	163	30
IMC and Water	inter-municipal AND cooperation OR collaboration OR intermunicipal AND cooperation OR collaboration OR inter-local AND cooperation OR collaboration OR interlocal AND collaboration OR cooperation AND water	Scopus and Web of Science	29	29
IMC and CE	inter-municipal AND cooperation OR collaboration OR intermunicipal AND cooperation OR collaboration OR inter-local AND cooperation OR collaboration OR interlocal AND cooperation OR collaboration AND “circular economy” OR reuse OR recycle OR replenish OR waste	Scopus and Web of Science	19	19
Search: on title, abstract, and keywords; limits: language (English), document type limits (articles); date: conducted on 19 September 2021; total 78 articles;

describes the steps used for the search and selection of articles.

The second step was dedicated to classifying the articles according to their approach to IMC. IMC is a multi-dimensional, diverse, and complex phenomenon [12]. On the one hand, IMC has been pursued by local governments as a strategy for public service delivery, driven by costs and economic efficiency and issues related to the governance structure and spatial context [18]. On the other hand, IMC is an approach that leads to sustainability [28], requiring the assessment of its impacts and sustainability rather than just economic benefits [16]. This study classified the articles (i.e., by identifying the articles dealing with these dimensions) from the databases into three dimensions, namely, governance (referring to institutional and governance arrangements and structures), service efficiency (referring to service performance, efficiency, cost, and fiscal factors), and, finally, impacts assessment (referring to the assessment of the impacts of IMC). 

Table 2. The three dimensions and their contents.

Dimensions	Contents
Governance	Institutional and governance arrangements and structures, political institutions and the structure of policy networks, policy, planning, geographic considerations, conflict resolutions, commitments and leadership, adaptive management;
Service efficiency	Scale and density, cost-saving, fiscal factors, transaction cost of IMC, different service delivery performance, the role of the IMC on the performance of local governments on services delivery;
Impacts assessment of IMC	Impacts of IMP, namely on different service delivery performance on environment, social context, or sustainability.

presents these dimensions.

The results of the literature review are presented in the following section. Firstly, they focus on the general characteristics of the literature identified for each database and how they are associated with the three dimensions. Secondly, they focus on emerging knowledge and gaps in the literature.

3. Findings

3.1. General Characteristics of the Literature Review

The evolution of publications under the three databases of the study (IMC, IMC and water, and IMC and CE) is shown in Figure 1. IMC is not a new topic; the first publication goes back to 1973. However, it has gained attention dramatically since 2006. Publications on IMC and water, and IMC and CE, on the other hand, are about to develop and have not increased considerably, indicating that there is plenty of room to explore and learn on these topics.

The most cited articles on IMC are concerned with two dimensions: first, service efficiency (53%); second, governance (47%) (Figure 2a). However, in the most recent articles, this ratio is a little different. The latest are dominated by service efficiency (53%), followed by governance (40%) (see Figure 2b). In addition, seven per cent of the articles are devoted to impacts assessment, emphasising the growth of the new emerging topic in the literature.

While there are just two qualitative studies among the newest articles, qualitative research methods are used in eight studies among the most cited articles by conducting a review of the literature or a comparative analysis. In contrast, quantitative research is more common among the newest articles (12 articles) than among the most cited ones (6 articles), indicating a growing tendency to use quantitative research methods. Estimating models, regression models, and panel data are the most used by quantitative studies. Finally, there are just two articles with mixed methodologies.

Articles crossing IMC and water reveal a dominancy of the governance dimension (55%), followed by service efficiency (35%), and impacts assessment (10%) (Figure 3a), reflecting the importance of governance, institutions, and policy networks in these studies. More than one-third of the articles are devoted to cost saving, fiscal factors, the transaction cost of IMC, and different service delivery performances. However, the number of studies on impacts assessment is limited. The growth in publications on all dimensions is nearly stalled (Figure 3b). Among the articles, nineteen are qualitative, applying document and policy analysis, six are quantitative, applying cost-benefit analysis, order-m, descriptive statistics, and regression models. Six articles conducted mixed research methods.

Articles crossing IMC and CE reveal a dominancy of service efficiency (58%), followed by governance (37%), and impacts assessment (5%) (Figure 4a), highlighting the importance of cost efficiency and fiscal concerns, in articles crossing IMC and CE. Nonetheless, 5% of studies are on impacts assessment. However, the number of publications regarding this dimension is growing, particularly after 2017 (Figure 4b). Unlike IMC and water, most studies on IMC and CE (13 articles) conducted a quantitative research method by applying several models, including order-m panel data, regression analysis, an F-test, the Ramsey-RESET test, the White test, and the Shapiro–Wilk test. There are just two qualitative and three mixed research methods studies within this database.

The findings show a higher number of articles on the governance and the service efficiency dimensions and fewer articles on the impacts assessment, showing the lack of focus of studies on the consequences of cooperation.

3.2. Emerging Knowledge and Gaps in the Literature

As mentioned in the previous section, the articles of the three databases (IMC, IMC and water, and IMC and EC) were reviewed and analysed according to three dimensions, namely governance, service efficiency, and, finally, impacts assessment. The next paragraphs present the major results.

3.2.1. Inter-Municipal Cooperation

The summary of the emerging knowledge and the gaps in the articles on selected IMC are presented in Table 3. Articles relevant to the governance dimension reveal that IMC is beneficial by enhancing regional coordination of municipal planning with a cross-jurisdictional and large-scale plan and a shared vision [29,30,31]. It also leads to solving administrative capacity problems (in smaller cities) [32] and reduces the threat of private developers (real estate) [14]. Apart from the benefits of IMC, a group of studies underscore several factors that must be considered for cooperation [17,31]. Regarding spatial concerns, studies show a strong connection between cooperation and land use and spatial features [18,32,33]. The choice of service delivery model (privatisation or cooperation) is affected by spatial characteristics [34]. IMC can increase the efficiency of land use planning, while territorial fragmentation may affect administrative outcomes by missing economies of scale [33]. Furthermore, cooperation for a specific policy related to new energies and climate change necessitates alignment with spatial planning as a critical tool for achieving a sustainable environment [35]. However, cooperation between different planning departments is still critical and challenging [30].

Articles relevant to the service efficiency dimension reveal that the success of cooperation can be affected by the size of the municipal population, the strength of political leadership and experienced managerial staff, and the perception of IMC by municipal officials [32]. Additionally, the roles of non-governmental stakeholders in cooperative governance networks must be acknowledged [25]. In addition, a smaller number of participants with a history of cooperation is more likely to enhance the commitment [36]. However, one group of researchers, for instance, refer IMC to be an efficient way of service provision [26,37,38,39], while another group did not find any significant impact of IMC on service efficiency [33,40]. Furthermore, the findings point out that fiscal constraints, spatial features, and organisational factors are significant drivers of cooperation [24].

Table 3. Summary of emerging knowledge and gaps in IMC articles.

	Knowledge	Gaps
Governance	- IMC offers cross-jurisdictional and large-scale plans and a shared vision [29,30,31] - IMC also leads to solving administrative capacity problems (in smaller cities) [32] - IMC reduces the threat of private developers (real estate) [14] - The success of cooperation can be affected by the size of the municipal population, the strength of political leadership and experienced managerial staff, and the perception of IMC by municipal officials [32] - Roles of non-governmental stakeholders in cooperative governance networks must be acknowledged [25] - A smaller number of participants with a history of cooperation are more likely to enhance the commitment [36] - IMC has the potential to improve the efficiency of land use planning [33] - The availability of space to construct infrastructure is important [35] - The dominancy of technical and traditional planning approaches limit cooperation [30];	- To explore factors for success and failure of co-operative arrangements [17] - To study on the role, capacity, and significance of city-regional actors [25] - To identify causal mechanisms for various types of cooperation [19] - To identify cause and effect of governance capacity value [31] - To measure the commitments of authorities [36];
Service efficiency	- IMC is an efficient form of service provision [26,37,38,39] - There is no significant effect of IMC on service efficiency [33,40] - Fiscal constraints, spatial, and organisational factors are significant drivers of cooperation [24] - Financial sustainability is critical for IMC arrangement and one of the most important drivers of cooperation [20,41] - Cooperation is more attractive and efficient for smaller municipalities [34,42];	- To test the benefits and efficiency of IMC [33,40,43] - To identify the model with the most efficient form of service delivery [38] - To explore all possible drivers of service delivery models [44] - To identify ways to reduce the transaction costs of cooperation [45] - To explore the relationship of the size asymmetry and service quality and autonomy costs [15] - To explore the relationship between local government financial health and the financial sustainability of IMC entities [20] - To explore more spatial and organisational factors in cooperation [24];
Impacts assessment	- IMC presents a critical factor for ensuring better environmental outcomes in metropolitan areas, as it facilitates policy coherence and widespread enforcement irrespective of the type of metropolitan governance structure [46].	- To explore the effect of cooperation on environmental outcomes [46].

Table 3. Summary of emerging knowledge and gaps in IMC articles.

	Knowledge	Gaps
Governance	- IMC offers cross-jurisdictional and large-scale plans and a shared vision [29,30,31] - IMC also leads to solving administrative capacity problems (in smaller cities) [32] - IMC reduces the threat of private developers (real estate) [14] - The success of cooperation can be affected by the size of the municipal population, the strength of political leadership and experienced managerial staff, and the perception of IMC by municipal officials [32] - Roles of non-governmental stakeholders in cooperative governance networks must be acknowledged [25] - A smaller number of participants with a history of cooperation are more likely to enhance the commitment [36] - IMC has the potential to improve the efficiency of land use planning [33] - The availability of space to construct infrastructure is important [35] - The dominancy of technical and traditional planning approaches limit cooperation [30];	- To explore factors for success and failure of co-operative arrangements [17] - To study on the role, capacity, and significance of city-regional actors [25] - To identify causal mechanisms for various types of cooperation [19] - To identify cause and effect of governance capacity value [31] - To measure the commitments of authorities [36];
Service efficiency	- IMC is an efficient form of service provision [26,37,38,39] - There is no significant effect of IMC on service efficiency [33,40] - Fiscal constraints, spatial, and organisational factors are significant drivers of cooperation [24] - Financial sustainability is critical for IMC arrangement and one of the most important drivers of cooperation [20,41] - Cooperation is more attractive and efficient for smaller municipalities [34,42];	- To test the benefits and efficiency of IMC [33,40,43] - To identify the model with the most efficient form of service delivery [38] - To explore all possible drivers of service delivery models [44] - To identify ways to reduce the transaction costs of cooperation [45] - To explore the relationship of the size asymmetry and service quality and autonomy costs [15] - To explore the relationship between local government financial health and the financial sustainability of IMC entities [20] - To explore more spatial and organisational factors in cooperation [24];
Impacts assessment	- IMC presents a critical factor for ensuring better environmental outcomes in metropolitan areas, as it facilitates policy coherence and widespread enforcement irrespective of the type of metropolitan governance structure [46].	- To explore the effect of cooperation on environmental outcomes [46].

The assessment of the cooperation is poorly covered by the articles, which suggests a gap in the knowledge.

3.2.2. Inter-Municipal Cooperation and Water

The findings related to the articles crossing IMC and water are summarised in Table 4. Articles dealing with the governance dimension refer that cooperation is a beneficial tool for water resource management [47,48,49]. Regarding spatial concerns, cooperation leads to a better use of water and land resources [13,48,50,51]. IMC makes effective land use for water management in terms of plant locations and transportation [47]. Remember that land use affects water quality [13]. The water system and urban structure are crucial for choosing a service delivery model (IMC or privatisation) [52].

However, articles dealing with the service efficiency dimension concluded differently. A series of studies cast doubt on the benefits of IMC, claiming that the benefits and impacts of IMC are unclear and must be explored and tested [11,21,22,23]. For instance, Zafra-Gómez et al., (2020) [53] conclude that IMC is not necessarily cost-efficient compared with direct public provision. In addition, Muraoka and Avellaneda (2021) [22] concluded that IMC positively affects electricity provision and has no significant effect on water provision. On the other hand, another group of studies confirms the benefits of IMC [54,55,56].

Table 4. Summary of emerging knowledge and gaps in articles crossing IMC and water.

	Knowledge	Gaps
Governance	- IMC arrangement creates (and has to ensure) a platform for engagement of all actors and stakeholders (public sector, researchers, citizens, and companies) [57,58] - IMC is more collective and transparent, benefiting from shared vision leading to harmonised development of urban infrastructures [50] - Cooperative approach facilitates addressing risks (technical, natural, and social) and trans-boundaries problems (environmental, etc.) [13,52,59] - IMC requires an establishment of: a strong leadership and communication, accompanied by ensuring the stakeholder’s engagement, which is shaped based on citizen perception, conflict solution, and problem solving [13,58]; an acknowledgement of risks including risks about institutional uncertainties (allocation of responsibility), transaction costs, and political costs for individual [59]; a high level of knowledge, competence, and commitment of those engaged in the process of delivering and regulating drinking water [59] addressing the challenges of local government such as the small size of municipalities and fiscal shortages [47]; enhancing political willingness to take actions in wastewater treatment introduces cooperative models as a reliable alternative [47] - IMC brings effective use of land for water management, in terms of locating plants and transport [47] - The water system and urban structure are important for choosing a service delivery model (IMC or privatisation) [52];	- To understand what an appropriate governance institutional form for each service, regarding the size of the population of municipalities [50] - To evaluate effects of IMC networks on other municipalities’ actions and activities and non-neighbouring interlocal arrangements [58] - To study collective action dilemmas in risk management [59] - To analyse several alternatives and choosing the most feasible one in local circumstances for water strategy [47];
Service efficiency	- IMC is beneficial in terms of administrative, and economic factors; IMC introduces an efficient model to address the local government problems (e.g., waste transportation costs, unclear and unfair pricing formation, etc.) [55] - To define joint goals and well-established institutional settings leading to better results in services provision [54] - To check the quality of services based on citizen perceptions [60] - To consider the size of the municipality population as a determinant factor for the success of the cooperation as it is more preferable for smaller municipalities [53,61];	- To explore and evaluate (viability, cost-efficiency) of different arrangements for public service provisions, regarding the contextual conditions [21,56] - To understand costs and prices of water in different arrangements [62] - To understand the economic and political factors of IA for public services [63];
Impacts assessment	- IMC is helpful to incentivise a sustainable urban transition [28].	- To assess sustainability and other effects of IMC rather than just its economic benefits [16].

Table 4. Summary of emerging knowledge and gaps in articles crossing IMC and water.

	Knowledge	Gaps
Governance	- IMC arrangement creates (and has to ensure) a platform for engagement of all actors and stakeholders (public sector, researchers, citizens, and companies) [57,58] - IMC is more collective and transparent, benefiting from shared vision leading to harmonised development of urban infrastructures [50] - Cooperative approach facilitates addressing risks (technical, natural, and social) and trans-boundaries problems (environmental, etc.) [13,52,59] - IMC requires an establishment of: a strong leadership and communication, accompanied by ensuring the stakeholder’s engagement, which is shaped based on citizen perception, conflict solution, and problem solving [13,58]; an acknowledgement of risks including risks about institutional uncertainties (allocation of responsibility), transaction costs, and political costs for individual [59]; a high level of knowledge, competence, and commitment of those engaged in the process of delivering and regulating drinking water [59] addressing the challenges of local government such as the small size of municipalities and fiscal shortages [47]; enhancing political willingness to take actions in wastewater treatment introduces cooperative models as a reliable alternative [47] - IMC brings effective use of land for water management, in terms of locating plants and transport [47] - The water system and urban structure are important for choosing a service delivery model (IMC or privatisation) [52];	- To understand what an appropriate governance institutional form for each service, regarding the size of the population of municipalities [50] - To evaluate effects of IMC networks on other municipalities’ actions and activities and non-neighbouring interlocal arrangements [58] - To study collective action dilemmas in risk management [59] - To analyse several alternatives and choosing the most feasible one in local circumstances for water strategy [47];
Service efficiency	- IMC is beneficial in terms of administrative, and economic factors; IMC introduces an efficient model to address the local government problems (e.g., waste transportation costs, unclear and unfair pricing formation, etc.) [55] - To define joint goals and well-established institutional settings leading to better results in services provision [54] - To check the quality of services based on citizen perceptions [60] - To consider the size of the municipality population as a determinant factor for the success of the cooperation as it is more preferable for smaller municipalities [53,61];	- To explore and evaluate (viability, cost-efficiency) of different arrangements for public service provisions, regarding the contextual conditions [21,56] - To understand costs and prices of water in different arrangements [62] - To understand the economic and political factors of IA for public services [63];
Impacts assessment	- IMC is helpful to incentivise a sustainable urban transition [28].	- To assess sustainability and other effects of IMC rather than just its economic benefits [16].

Regarding the impacts assessment dimension, Neumann and Hack, (2019) [28] declared that IMC is helpful to incentivise a sustainable urban transition. However, rather than just the economic benefits of IMC, its other impacts and sustainability must be assessed [16].

3.2.3. Inter-Municipal Cooperation and Circular Economy

The findings of studies crossing IMC and CE are summarised in Table 5. Articles relevant to the governance dimension reveal that waste management calls for a cooperative governance model (among different sectors and in central cities and smaller ones) [64,65,66]. Furthermore, this cooperation requires strong political will at the local level and longer-term agreements [67]. Therefore, there is a need to investigate the factors affecting the choice of municipalities to choose IMC for solid waste management and to study the optimal definition of the geographic boundaries of IMC [27,67]. Regarding spatial concerns, the studies highlight the significance of spatial concerns on the model and the cost of water services [64,68,69]. Adequate municipal infrastructure depends on the collection, transportation, and disposal, highlighting the importance of spatial aspects [68]. Furthermore, the spatial population distribution influences the waste service cost [69].

However, articles relevant to the service efficiency dimension acknowledge the cost-efficiency of IMC as the key motivation for choosing this model in municipal solid waste service delivery [70,71,72]. Similar to other databases in this study, the topic of impacts assessment received poor attention, calling for more studies in future.

Table 5. Summary of emerging knowledge and the gaps on articles crossing IMC and CE.

	Knowledge	Gaps
Governance	- Waste management needs collaborative governance (among different sectors and central cities and smaller ones) [64,65,66] - IMC is not necessarily cost saving [73] this cooperation requires a strong political leadership at the local level and longer-term agreements [67] - IMC can be a rational choice for smaller municipalities (under 55000 population); increasing the population over that leads to worsening the efficiency [67] - To consider that the spatial distribution of population on space affects the costs of waste service [69];	- To study the optimal definition of the geographic boundaries of IMC [27,67];
Service efficiency	- The size of the municipal population is an important factor for cooperation seeing that IMC is more popular among small and mid-size cities [69,71,74,75,76] - IMC addresses the financial burden of local governments [70] - IMC brings economies of scale [70,72] - IMC is cost saving in waste collection [77] - IMC makes a platform to share experience, knowledge, and information [74,77] - Cooperation raises collection frequency and improves the quality of the service in small towns [69] - IMC involving spatial interaction with neighbouring municipalities influences the decision making and collaborative action of municipalities to implement recyclables collection and reduce costs [78];	- To understand factors affecting public service costs [70] to extend the IMC studies for different sectors and services [70] - To understand how institutional mechanisms can lead to cost efficiency [74,76],
Impacts Assessment	- Small municipalities may seek IMC and adopt integrated waste-management programmes to reduce their environmental impacts [68].	- To analyse economic aspects next to the analysis of potential energy and GHG emissions [68].

Table 5. Summary of emerging knowledge and the gaps on articles crossing IMC and CE.

	Knowledge	Gaps
Governance	- Waste management needs collaborative governance (among different sectors and central cities and smaller ones) [64,65,66] - IMC is not necessarily cost saving [73] this cooperation requires a strong political leadership at the local level and longer-term agreements [67] - IMC can be a rational choice for smaller municipalities (under 55000 population); increasing the population over that leads to worsening the efficiency [67] - To consider that the spatial distribution of population on space affects the costs of waste service [69];	- To study the optimal definition of the geographic boundaries of IMC [27,67];
Service efficiency	- The size of the municipal population is an important factor for cooperation seeing that IMC is more popular among small and mid-size cities [69,71,74,75,76] - IMC addresses the financial burden of local governments [70] - IMC brings economies of scale [70,72] - IMC is cost saving in waste collection [77] - IMC makes a platform to share experience, knowledge, and information [74,77] - Cooperation raises collection frequency and improves the quality of the service in small towns [69] - IMC involving spatial interaction with neighbouring municipalities influences the decision making and collaborative action of municipalities to implement recyclables collection and reduce costs [78];	- To understand factors affecting public service costs [70] to extend the IMC studies for different sectors and services [70] - To understand how institutional mechanisms can lead to cost efficiency [74,76],
Impacts Assessment	- Small municipalities may seek IMC and adopt integrated waste-management programmes to reduce their environmental impacts [68].	- To analyse economic aspects next to the analysis of potential energy and GHG emissions [68].

After investigating and analysing the literature, the essential considerations, requirements, and concerns for local government cooperation for WCE are summarised in

Table 6. Summary of the findings: learnings and gaps from IMC and WCE.

Governance	- To enhance the governance capacity, build strong leadership, train the local administrative staff, build trust, and increase transparency [50,52] - To ensure the participation of all actors and stakeholders, (public actors, private sectors and developers, citizens, and researchers) [57,58]; - To consider that cooperation is rooted in space [18] and land use and spatial features matter for a successful cooperation [18,32,33,68,69], also, to adopt a cross-boundary approach articulating land use and water resources management [13] - To adopt a co-creation approach to co-find and co-solve the problems [13] - To improve a platform for sharing knowledge and experiences, for communicating and negotiating [13,14] and to establish a joint goal and shared vision [50] - To identify and understand transboundary risks and institutional risks of cooperation [19,59] - To include the citizen perception in the service delivery assessments [60] - To understand the cooperation on a bigger scale and to identify its effect on neighbours [78];
Service efficiency	- To test and analyse the cost efficiency of IMC before reforming into it [22,23] - To analyse the quality and price of services at the cooperation governance [62] - To ensure achieving financial sustainability after cooperation [20] - To understand the size asymmetry, service characteristics, contextual conditions, fiscal constraints, and organisational factors for choosing the best arrangement [15,23,44] - To adopt an ongoing process on reducing the transaction costs of cooperation [45];
Impacts assessment	- To assess the sustainability of the chosen institutional arrangement for services [16] - To ensure that the cooperation leads to better social and environmental outcomes [46] - To adopt a coherent approach considering climate change, population growth, and regulatory restrictions to analyse the arrangement alternatives [79].

.

Considering the results of the literature review, the success of IMC for the adoption of WCE requires the simultaneous consideration of a set of governance practices, the analysis and testing of cost efficiency and guaranteeing financial balance, and the assessment of social and environmental consequences. Nevertheless, these dimensions are not equally addressed by the literature. While governance and efficiency are often referred to, the assessment of IMC experiences in the context of WCE is still poorly explored.

4. Discussion and Conclusions

The transition towards a WCE may generate new risks and challenges to water governance associated with qualities of water, spatial issues (for storing and transporting, for instance), and new sets of actors involved. This transition is challenging and IMC may be a valuable governance arrangement to facilitate future steps. IMC is known to enhance synergies between agencies, stakeholders, and different spatial contexts [47,50,57,58].

After developing a review of the literature, the findings of this article offer an evidence-based insight about the emergence of IMC as a potentially appropriate governance model for implementing WCE. Adopting WCE in the context of IMC requires simultaneous attention to all three dimensions, namely governance (e.g., benefiting from shared goals, visions, knowledge, experiences, co-creation process, and acknowledgement of risks), service efficiency (e.g., benefiting from the more cost-effective performance, a fair pricing system, economics of scale and scope, fiscal sustainability, and lower transition cost of cooperation), and impacts assessment (benefiting from an assessment of social, economic, and environmental outcomes). Nevertheless, the findings show that although governance, efficiency and impacts assessment are key dimensions pursued under IMC approaches, few studies appear in the scientific community assessing experiences of IMC in the context of water management and WCE. Consequently, it is still difficult to assess whether IMC is indeed suitable for WCE. Further studies are needed on this topic.

Regarding the governance dimension, IMC can not only enhance the governance capacity and engagement of different types of stakeholders by making a transboundary platform to share goals, visions, knowledge, and experiences but also must ensure the co-find and co-solve (co-creation) of transboundary problems, which are usually outside the potential of a single fragmented municipality [13,14]. In addition, cooperation, land use, and spatial characteristics are closely related [18,32,33]. In terms of plant location and transportation, IMC can provide an effective use of land for water management [47]; considering that, the water system and the urban form are important for choosing a service delivery model (IMC or privatisation) [52]. For WCE, infrastructure development for reusing water (treatment, storage, transportation, etc.) needs space. Furthermore, the spatial distribution of the population influences service delivery costs and the demand for cooperation [68]. The distribution of the population in a space affects the cost of waste service more than the size of the population [46,69]. However, IMC has several disadvantages, including difficulties in boundary-crossing coordination, weak sanctioning, diversity in geographic location, political transaction costs [24], and decreasing democratic legitimacy and transparency [42]. Regarding the service efficiency dimension, cooperation among local governments is beneficial by achieving economies of scale, enhancing service quality, and addressing issues caused by fragmentation and fiscal limitations [18,26]. However, the cost-efficiency of IMC needs to be tested [22,23]. Additionally, IMC must guarantee the reduction of transaction costs and financial sustainability [20,45], in particular for the adoption of WCE. Regarding the impacts assessment dimension, although IMC helps achieve sustainability [28], the impacts of cooperation on environmental outcomes must be assessed [16,46].

This review of the literature was based on a strict set of methodological steps and the retrieved articles on the major topics (IMC and WCE). It was developed through the classification of articles into three dimensions. Although using a qualitative classification based on the articles’ approaches, no mismatches were found, making the findings consistent for analysis. Due to the scarcity of studies on IMC and WCE, it used three databases covering IMC, IMC and water, and IMC and CE. The WCE adoption, in the sense of water reuse, is a recent matter at the European and national policy and management levels. In addition, the involvement of municipalities in its implementation is only recently gaining momentum. This may explain the limited number of articles relating to WCE and IMC.

This study focused on IMC as one governance arrangement to deal with various challenges of water management. The findings are useful for future research on institutional arrangements for the governance of WCE considering the potential of IMC. Still, the results are only based on a review of the literature. Further case-based analysis would extend these findings to real-world scenarios, enriching our understanding of the potential and the limitations of IMC for WCE adoption. It might also provide useful information and outcomes for expanding various national contexts.