The Brussels Air, Climate and Energy Code (CoBrACE) is responsible for general climate action. Regarding water bodies, the Plan Communal Eau (Water Management Plan) addresses all water management issues, including those relating to rivers, ponds, drinking water supplies, groundwater and flooding. The Ordinance on the Organisation of Thermal Energy Networks and Measuring Thermal Energy Consumption establishes a legal framework for the organisation of thermal energy networks (i.e. heating and cooling networks) and the measurement of thermal energy consumption, thereby addressing AQE. However, legislation regarding discharges and extractions from surface water for thermal use and its interpretation is not specified in detail. While there is some existing framework around AQE, it is currently limited to the use of cooling water. Heating with AQE is not regulated. Furthermore, the Environmental Impact Assessment Ordinance for Certain Plans and Programmes establishes a framework for granting future project permits and enables the government to decide whether a plan or programme may have significant environmental effects. Unfortunately, a lack of political support hinders the development of AQE, and changes in government have resulted in new climate policies lacking long-term vision, which may also discourage AQE.

Brussels provides funds and support for investment and individual projects, but not for AQE or heating issues specifically. The current low price of gas makes alternative technologies, such as AQE, less financially attractive, leading to an unfavourable price ratio for heat pump technologies. Additionally, the significant upfront costs of AQE infrastructure and district heating systems pose a financial barrier, especially since investment subsidies are not available at the level of the Brussels-Capital Region, only co-financing is available.

The permitting process takes up to one and a half years, but the exact timelines are unclear, and extensions are possible. Costs can amount to several thousand euros and can be difficult to estimate. The large number of permits and unknown requirements lead to increased complexity, and the interdependencies between the different authorities pose a risk of delay. The predominance of individual heating choices that do not align with AQE can hinder the development of district heating networks, as can the lack of clarity surrounding AQE regulations. Bruxelles Environnement has only developed a limited framework and AQE has not yet been integrated into the broader sustainability vision.

Brussels, engaged stakeholders are the authorities responsible for water management. In addition, Innoviris.Brussels provides subsidies for the implementation of new heat network technologies and Ecobuild.Brussels is a network of sustainable and circular construction and renovation actors.

Local policy is a barrier to AQE development as it lags behind advancements in AQE regulation. Additionally, public perception remains low, and the potential of AQE is generally unknown and underestimated. Many consultancy firms are questioning its financial and technical feasibility due to a lack of practical examples and knowledge. Providing more practical applications and information could raise awareness and reduce the risk of public resistance.

It is unclear whether there are any upcoming projects aimed at assessing the potential of AQE or creating clearer regulations.

In general, though, there is high potential for improvement if the regulations regarding AQE, district heating network, and types of permitted infrastructure are clarified, and if a favourable legal framework concerning urban planning and environmental regulations for the installation and operation of heating networks, including AQE, is established. Financial support must be increased and capture fees decreased. Investment in AQE needs to increase, but the price difference between gas and electricity creates a financial obstacle, threatening heat-pump-based technologies. Subsidies would encourage AQE uptake. Furthermore, a lack of political support and incomplete policies hinder the development of AQE. Single case treatment is time-consuming; therefore, developing a tool to streamline and clarify application procedures would help realise AQE’s potential. Authorities working on AQE-related policies and integrating them into heat zoning plans will contribute to environmental goals such as those outlined in the National Energy and Climate Plan (NEKP), Belgium's framework for achieving European energy and climate goals.

However, ignorance of the technology itself, distribution issues, and regulatory uncertainty pose a structural threat to AQE deployment. Therefore, full AQE integration is essential. In general, heating needs to become a more collective effort, rather than being based on individual heating choices. More AQE examples and knowledge would benefit public acceptance and increase awareness of the environmental benefit.

There are 10 existing projects in Belgium, and 48 additional projects are currently planned.

The ecological impact of AQE for both heating and cooling is not yet fully understood. Furthermore, the framework for heating networks in Brussels is limited. Consequently, AQE developments are resource-intensive, as the infrastructure of each case is examined individually by the watercourse manager.

Flanders has a climate action plan, the Vlaams Energie en Klimaatplan, [IS1] that aims to mitigate the effects of climate change and accelerate the transition to a low-carbon economy. The Kaderrichtlijn water (water code) provides an overarching legal framework for all water management rules and principles, while the River Basin Management Plans are specific to river basins. The latter's objective is to maintain and improve the quality of surface water and groundwater, prevent flooding and drought, and encourage the sustainable use of water. Furthermore, Flanders is working on a spatial structure plan for AQE for which the province of East Flanders has served as a pilot region (ruimtelijk beleidsplan). Additionally, local energy and climate plans support municipalities and cities in addressing the challenges of climate change at a local level. However, legislation and its interpretation in Flanders relating to the discharge and extraction of surface water for thermal use are not always clear or straightforward. Legislation relevant to AQE was created for use in other sectors, resulting in a framework that is less applicable to AQE. However, the regulatory framework is currently under development.

Spatial and energy policies in Flanders are incoherent with regard to AQE, and testing is absent from the existing energy policy. However, a study examining the potential of AQE and the link between energy and spatial integration is currently being conducted. This will include an analysis of the most suitable locations for AQE, taking into account spatial features such as critical natural zones, types of energy consumers, and areas of high population density.

In Flanders, only general funds and programme support for green innovations are available. The Flemish government provides subsidies for heat pumps in renovations and offers investment support through its "Call for Green Heat" programme for those investing in new green heat, residual heat or energy-efficient district heating projects. Additionally, private companies receive support from the GREEN investeringssteun (Green Investment Fund). Despite this investment support, the price ratio between natural gas and electricity is high (gas is four times cheaper than electricity per unit), which makes AQE less attractive. The investment cost of infrastructure and AQE heat networks is high, and there is no financing available for the study costs of AQE developments. Moreover, subsidies for heat networks are limited. Additional investments are required to make a building heat pump-ready, and levies and taxes apply. Finally, the capture fee payable to De Vlaamse Waterweg (Flemish Waterways) makes AQE less financially attractive when extracting water from navigable waterways.

The permitting process takes about half a year, but an extension due to revaluation is possible. Costs can range from a few hundred to a few thousand euros, depending on the size of the project. However, AQE faces a challenge due to inconsistencies and a lack of homogeneity between different watercourse managers. In terms of procedural clarity, the CIW (a Flemish waterway organisation that also works on AQE) operates entirely informally within the current framework. The CIW aims to clarify and improve the practical applicability of the AQE policy. It will also provide recommendations in 2026 on how AQE can be incorporated into a formal framework.

Challenges include the distribution of heat from water, uncertainty in urban planning about underground constructions, and the availability of water and potential. There is an information gap, and the potential of AQE is either unknown or underestimated. In the future, issues regarding the distribution of heat in public water bodies may arise; currently, the 'first come, first served' approach is used. So far, Flanders has adopted a very individual approach to heating, whereas AQE is more suitable for collective heating.

Cities, municipalities and provinces in Flanders are considering using AQE as a source of clean heat for their heritage sites and territories. Energy brokers (energiemakelaars) and energy cooperatives are communities that share experience and knowledge, and that work together. Additionally, the CIW, organised by the Flemish Waterways, is a specific structure that organisations such as the Environmental Agency and the provinces are part of. However, local AQE policies are lagging behind and failing to keep pace with advancements in the field. Additionally, public perception remains low, with the potential of AQE being generally unknown and underestimated. Furthermore, many consultancy firms are questioning their financial and technical feasibility due to a lack of practical examples and knowledge. Providing more practical applications and information could raise awareness and reduce the risk of public resistance.

A study is being conducted to map the potential for AQE across the Flemish region. Governmental authorities, such as De Vlaamse Waterweg and the Vlaamse Milieumaatschappij (Flemish Environmental Agency), are also developing policies related to AQE. Furthermore, AQE has been incorporated into heat zoning plans, with the prospect of it becoming a reliable and accepted technique.

In general, there is high potential for improvement if the regulations regarding AQE, district heating networks, and types of permitted infrastructure are clarified, and if a favourable legal framework concerning urban planning and environmental regulations for the installation and operation of heating networks, including AQE, is established. Financial support must be increased and capture fees reduced. Investment in AQE needs to increase, but the price difference between gas and electricity creates a financial obstacle, threatening heat-pump-based technologies. Subsidies would encourage AQE uptake. Furthermore, a lack of political support and incomplete policies hinder the development of AQE. Single case treatment is time-consuming; therefore, developing a tool to streamline and clarify application procedures would help realise AQE's potential. Authorities working on AQE-related policies and integrating them into heat zoning plans will contribute to environmental goals such as those outlined in the National Energy and Climate Plan (NEKP), Belgium's framework for achieving European energy and climate goals.

However, lack of awareness, distribution issues, and regulatory uncertainty pose a structural threat to AQE deployment. Therefore, full AQE integration is essential. In general, heating needs to become a more collective effort, rather than being based on individual heating choices. More AQE examples and knowledge would benefit public acceptance and increase awareness of the environmental benefits.

There are 10 existing projects in Belgium, and 48 additional projects are currently planned.

The ecological impact of AQE for both cooling and heating is not yet fully known. Until more information on its impact on the water body is available, Flanders tends to adopt the worst-case scenario. Furthermore, there is only a limited framework for heating networks. As a result, AQE developments are very intensive, since the infrastructure of each case is individually examined by the watercourse manager.

The Covenant of Mayors in Wallonia is part of a broader European initiative, whereby local authorities pledge to reduce CO₂ emissions and address climate change mitigation in accordance with the Walloon Air, Climate and Energy Plan. The General Regulation on Classified Installations  of Wallonia includes provisions for classifying and granting permits for installations that may have an environmental impact, including those related to AQE. The Code de l'Eau (Water Code), which is part of the Environment Code, regulates water use and management. This includes provisions relevant to the utilisation of water bodies for thermal energy extraction. The Walloon Environmental Code of 27 May 2004 establishes the framework for environmental legislation on topics such as water, waste, and environmental permits.

The Water Code requires the protection of water bodies, which could limit the exploitation of these resources for AQE purposes. This may conflict with regional targets to maximise the use of renewable energy sources, as set out in the Plan Air Climat Énergie. Furthermore, the Walloon regulatory framework may not always keep pace with technological advancements in AQE, leading to situations where innovative AQE technologies face outdated or overly restrictive regulations that hinder their deployment. The lack of clear Walloon standards, legislation and guidelines for AQE complicates its implementation further. Additionally, the continued use of gas in new residential developments in Wallonia acts as an obstacle to the development of AQE. The current energy policy in Wallonia lacks coherence in terms of spatial and energy policy, and spatial planning and testing are absent.

Wallonia organises specific calls for green projects. For instance, there is currently an open call for projects that support the development or expansion of thermal energy networks. The region promotes sustainable energy solutions by financing projects that optimise energy distribution and reduce CO₂ emissions. Furthermore, financial support is available for energy efficiency and renewable energy projects.

A barrier to AQE development is the price ratio between natural gas and electricity (gas is priced at four times the rate of electricity). The costs of AQE infrastructure and heat networks are high, and no financing is available to cover the costs of developing AQE. Furthermore, subsidies for heat networks are limited. Additional levies and taxes pose a further barrier to AQE. A capture fee reduces the financial incentive for extracting water from navigable waterways.

Obtaining permission in Wallonia takes about half a year, but an extension by revaluation is possible. Permission costs can amount to a few thousand euros, with additional unknown costs. The number of authorities involved, as well as the interdependencies and inconsistencies between them, increases the complexity of the process and the risk of delays. There are specific regional regulations and limits on the discharge of non-domestic wastewater, including cooling water. Generally, a lack of information can result in the potential for AQE being unknown or underestimated. For issues related to the distribution of heat in public water bodies, the 'first come, first served' approach is currently in place. So far, Wallonia has a very individual approach to heating, whereas AQE is more suitable for collective heating.

Several authorities provide support and guidance on sustainable energy, including AQE and water management. These authorities include the Walloon Association for Sustainable Energy, the AWAC (Walloon Agency for Air and Climate), the Walloon Energy and Sustainable Building Department and the (Wallonia Public Service). Barriers to AQE development include local policies that lag behind in terms of AQE regulation, failing to keep pace with advancements in the field. Additionally, public perception remains low, and the potential of AQE is generally unknown and underestimated. Furthermore, many consultancy firms are questioning its financial and technical feasibility due to a lack of practical examples and knowledge. Providing more practical applications and information could raise awareness and reduce the risk of public resistance.

It is unclear whether there are any upcoming projects aimed at assessing the potential of AQE or creating clearer regulations.

In general, though, there is high potential for improvement if the regulations regarding AQE, district heating networks, and types of permitted infrastructure are clarified, and if a favourable legal framework concerning urban planning and environmental regulations for the installation and operation of heating networks, including AQE, is established. Financial support must be increased and capture fees reduced. Investment in AQE needs to increase, but the price difference between gas and electricity creates a financial obstacle, threatening heat-pump-based technologies. Subsidies would encourage the AQE uptake. Furthermore, a lack of political support and incomplete policies hinder the development of AQE. Single case treatment is time-consuming; therefore, developing a tool to streamline and clarify application procedures would help realise AQE’s potential. Authorities working on AQE-related policies and integrating them into heat zoning plans will contribute to environmental goals such as those outlined in the National Energy and Climate Plan (NEKP), Belgium's framework for achieving European energy and climate goals.

However, lack of awareness, distribution issues, and regulatory uncertainty pose a structural threat to AQE deployment. Therefore, full AQE integration is essential. In general, heating needs to become a more collective effort, rather than being based on individual heating choices. More AQE examples and knowledge would benefit public acceptance and increase awareness of the environmental benefits.

There are 10 existing projects in Belgium, and 48 additional projects are currently planned.

The ecological impact of AQE for both heating and cooling is not yet fully understood. Furthermore, the framework for heating networks in Wallonia is limited. Consequently, AQE developments are resource-intensive, as the infrastructure for each case is examined individually by the watercourse manager.

France has implemented the PCAET, a six-year plan for cities to commit to climate change mitigation and adaptation action for residents. Furthermore, the Guide PAC eau de mer (seawater heat pump guide) outlines all the key elements for the development and operation of an effective seawater heat pump project. ADEME (agency for ecological transition) issues a national grant and provides technical assistance in the form of checking compliance with regulations, creating knowledge consortia when needed and final validation of the project.

A key contradiction in French policies is the 5°C temperature delta for water discharge, despite the possibility of altering it to 20°C for industrial purposes. Furthermore, most areas along rivers are subject to flooding (PPRL). The legislation states that it is not possible to build an energy production unit serving people outside the affected area. However, this law does not apply to a hydrogen station in a high-risk flood area that serves non-flood zones, for instance. There are gaps in the French regulations and insufficient detail regarding extraction methods, environmental aspects, multi-energy technologies and viable business models. Ongoing discussions about protecting water bodies might challenge AQE and hinder its development. Moreover, most political changes in recent years have negatively impacted the budgets allocated to developing renewable energies. Additionally, politicians are poorly informed and reluctant to adopt this relatively new technology.

The Fonds Chaleur (heat fund) provides grants of up to 80% for renewable heat projects (geothermal, wood, solar and district heating grids), but these are only available to public authorities or private entities with a SIRET number. Then, project owners can contact ADEME directly or their local representative, the 'territorial renewable heat contract coordinator'. Additionally, there are several citizen funding networks (Lumo Investments, Energie Partagée and Taranis) that empower citizens around renewable energy projects both financially and through active participation in fundamental discussions that make up a sustainable, shared energy transition.

Nevertheless, financial barriers are numerous, as there is no specific financial aid mechanism for AQE. Thus, subsidies can only be obtained via various permits and are limited, as the risk for AQE tends to be overestimated. Consequently, only large companies with substantial financial resources can afford to develop them (IDEx, Dalkia, Engie, etc.). In addition, current electricity prices (based on nuclear energy) and gas prices discourage the use of renewable energies.

The permit process takes up to two years, as processing times can be estimated, except for archaeological diagnosis. An operating licence costs between 20,000 and 30,000 euros, and a declaration file costs 15,000 euros. Generally, non-transparent information hinders an overall cost estimation. The large number of permits and their interdependency led to increased complexity. In addition, long validation periods and interdependencies pose a risk. Overall, the regulations are adapted to renewable energies, but not to AQE. Thermal design offices tend to focus on geothermal heat, and experts are unaware of AQE technologies.

Public authorities (ADEME, DREAL) are involved in promoting a sustainable energy transition. Community-led approaches, including AQE, could accelerate the green energy transition; therefore, misinformation represents a high risk. People imagine pipes on their beaches or in their harbours and expect disturbance to the oceans. Therefore, citizens’ groups have been set up to protest against AQE projects.

In the short term, a few AQE projects are planned on a small, local scale, such as the construction of wellness centres in cities like Lorient. These projects could serve as leading examples of best practice, and additional large-scale projects are currently emerging. More projects are also needed, especially those that can serve as best-practice examples, to facilitate regulatory change based on an updated evaluation of risks of AQE since current regulations and risk evaluations threaten future development.

In the long term, however, structural changes are required for AQE to play an essential role in the renewable energy transition. The active inclusion of AQE in political regulations and support structures would allow for simplified project implementation. Clearer environmental guidelines and standards (e.g., for delta T) would fasten the environmental impact assessments and improve infrastructural possibilities. However, environmental barriers such as protected areas will likely remain in the future. Furthermore, ADEME could relax its criteria for obtaining a grant to develop an AQE system, and access to AQE-specific funds, subsidies and access to further existing financial support structures needs to be facilitated for an expansion. The risk that financial aid remains non-AQE-specific threatens future projects. Additionally, the capacity of thermal design offices and their willingness to include AQE in their services represent a structural barrier threatening AQE development. Misinformation also poses a risk to AQE and must be reduced to improve the acceptance and demand for AQE in community-led systems. Therefore, NGOs could play a role in communicating and providing information about AQE to reduce misinformation and empowering people to implement community-led projects. Finally, AQE could benefit ADEME and DREAL in achieving climate change resilience and sustainability measures, as it is a sustainable heat source that should form part of the future renewable energy mix.

Germany has adopted a climate protection law (Klimaschutzgesetz), legally committing the country to achieving greenhouse gas neutrality by 2045 through a comprehensive climate strategy. To support this, the Wärmeplanungsgesetz (Heat Planning Act) requires all municipalities to develop comprehensive municipal heat plans (Kommunale Wärmeplanung) by 2026 and 2028, respectively. These plans must include an assessment of existing heat supply structures and the potential for renewable energy sources, including AQE. Furthermore, the law sets national targets for grid-based heat from renewable sources or unavoidable waste heat. The Gebäudeenergiegesetz (Building Energy Act) actively promotes renewable energy sources, encouraging communities to adopt renewable energy technologies. Additionally, the Kommunalrichtlinie (a municipal guideline) supports municipalities in reducing their emissions sustainably by providing funding for feasibility studies, consultancy services, municipal networks and energy-saving models.

However, AQE remains poorly defined in existing regulations. Specifically, while it is defined how much water bodies can be cooled down, it is not defined how much they can be heated up. Furthermore, there are no established standards to determine how much of a waterbody’s thermal capacity can be used or how close subsequent AQE systems can be installed along flowing water. Additional barriers arise from slow policy standardisation and limited political communication. Due to low public visibility and perceived environmental risks, which are often exaggerated in the absence of reliable data, policymakers tend to underestimate AQE’s potential. Nevertheless, the development of the political agenda influences the information and communication on the topic.

The state development bank offers grants and loans for renewable energy and heating systems, but there is no specific funding available for AQE. Although a national grant for efficient heating networks exists and various regional funding schemes are available, access often depends on project-specific evaluations and the decisions of local authorities. Furthermore, the high initial costs of implementation and infrastructure continue to present a significant financial obstacle to the deployment of AQE.

The duration of the permitting process is unclear, but it is estimated to take a total of two years. The permitting fees are also unclear, and the process is further complicated by the unknown responsibilities of the relevant administrations. There are no standardised procedures, as the application of regulations and policies varies depending on the local authority. The law does not specify temperature thresholds or a list of refrigerants that require an Environmental Impact Assessment (EIA). However, changes in the overall temperature of the body of water are assessed as part of the EIA. In result, long validation periods and slow procedural changes pose a barrier to AQE project development, as there is no general approach that the authorities can consistently follow and processes diverge across regions. Applications are more likely to be rejected when regulations are unclear, extensive or complex.

An increasing number of research institutions are engaged in AQE projects, including the Technical University of Darmstadt and the Fraunhofer Institute. At the regional level, stakeholders are represented by actors such as the Landesenergieagentur (regional energy agency).

Although public scepticism remains due to a lack of information, this can be reduced in the long term through education and demonstration. For instance, the Kompetenzzentrum Kommunale Wärmewende (KWW) promotes communication and engages with communities to facilitate the heat transition.

AQE faces significant structural barriers due to unclear administrative responsibilities, fragmented standards and the absence of national guidelines. However, if regulations and governance structures were to be standardised across the country, AQE could contribute significantly to achieving climate neutrality by 2045. Removing barriers to implementing new infrastructure and paying more attention to AQE in the renewable energy mix are essential.

The ongoing development of support structures, combined with decreasing costs for AQE relative to fossil-based systems, would further reduce financial barriers and make it a more attractive option.

Unfortunately, progress is slow and political agendas heavily influence public communication, often amplifying perceived risks due to a lack of information, which threatens the development of AQE. Increased public education and the availability of information, as well as stronger political will, are crucial to overcoming scepticism and prejudices towards environmental impact, and to advancing AQE deployment.

Nevertheless, research institutions, energy authorities and renewable energy experts recognise the significant technical and environmental potential of AQE, especially given Germany’s abundant water resources. In addition, the kommunale Wärmeplanung provides a framework for evaluating local conditions and requires municipalities to develop heat plans by 2026 for cities with over 100,000 inhabitants and by 2028 for smaller municipalities. These plans are technology-neutral and encourage diverse renewable solutions, including district heating, heat pumps and climate-neutral gases. The law also sets clear targets: by 2030, half of all grid-based heating should be climate-neutral, with renewable or waste heat contributing at least 30% by 2030 and 80% by 2040. While this creates opportunities for AQE integration, the absence of AQE-specific regulations could benefit well-established technologies.

Ireland has implemented a Climate Action Plan which sets out the goal of providing 2.7 TWh of district heating per year by 2030, with AQE potentially being a key source. The government additionally aims to enable Ireland to transition to a low-carbon, climate-resilient and environmentally sustainable economy within EU and global frameworks. By 2030, it intends to meet the targets of up to 80% renewable electricity, a 30% reduction in CO₂ emissions and a 32.5% improvement in energy efficiency. While Ireland's policies and frameworks relate to renewable energy, heating and cooling, none of them mention AQE directly. This is expected to cause issues with the rollout of AQE. Furthermore, if policy and financial support for AQE development are too slow and there is a lack of focus on this area, regulations will remain a major barrier to its implementation.

The Climate Action Fund is a general financial support in Ireland. Financial barriers affect research funding, planning and feasibility funding, and capital investment.

Little is known about the permits, their requirements, validation criteria, costs or processing times. There is no direct mention of AQE implementation procedures in Ireland. Structural barriers to the development of AQE include a lack of information, resources, experts, services and developers.

Engaged stakeholders include the authorities responsible for water bodies and water-related management, as well as the local community, who can provide an important support for the energy transition. However, more information needs to be provided to raise public awareness, as a lack of awareness may lead to resistance.

The development of regulations, governance structures and policies for AQE could contribute significantly to the achievement of the country's climate protection targets by 2030. Targets relating to district heating already exist within the next 20 years (up to 2.5 TWh/year for residential buildings and up to 0.2 TWh/year for public and commercial buildings), as set out in the Climate Action Plan. Promoting the potential of AQE and including it in policies as a source of district heating would benefit its future development, as well as encouraging a focus on small-scale, local district heating systems. Case studies and proof of feasibility could encourage further AQE implementation.

However, the current lack of information, resources, experts, services and developers structurally threatens AQE development. AQE potential must also be increased by environmental regulatory policies. Improving financial support structures for AQE is essential, as current barriers include research funding, planning and feasibility funding, and capital investment. A political shift towards environmental targets would increase focus on AQE objectives, and greater awareness of the topic could be raised.

The Project Ireland 2040, a national planning framework, is currently under discussion. The Project Ireland 2040 Delivery Board is a non-statutory board which provides strategic direction and leadership for the implementation of the National Development Plan (NDP) and National Planning Framework (NPF). There is high potential to reach the district heating targets through AQE, which would contribute to the Climate Action Plan and the transition to a low-carbon, climate-resilient and environmentally sustainable economy.

In the Netherlands, the CO2 reduction goals, including achieving climate neutrality by 2050, are set out in the Klimaatakkoord, which encourages the transition to renewable energy. Policies promoting AQE currently exist only at a regional level. The Missy Wetterwaarmte is a Frisian programme designed to stimulate the adoption of collective AQE systems, providing project development support and enhancing standardisation with the target of 20% of buildings heated collectively in Frysland by 2030. However, there are policy gaps: Low-temperature heat is not considered as heat, meaning it has no tariff structure, which hinders the creation of a business case. Furthermore, the depreciation rates for collective systems are limited to 25 years, but a longer timeframe would be required. A District Heating Law is still under discussion and poses a barrier to AQE development. Additionally, the affordability of district heating poses a policy risk. Although gas will be phased out in the long term, it is presently used as a point of comparison with district heating network prices.

A variety of funds and subsidies are available to encourage sustainable development, renewable energy, heating solutions and CO₂ reduction. While some of these are specifically aimed at district heating solutions, such as WIS (heat networks investment subsidy) and Proeftuinen Aardgasvrije Wijken (test beds for natural gas-free neighbourhoods), none of them are AQE-specific. However, insufficient development and implementation capacity pose a financial barrier to AQE implementation, particularly given that the development of district heating networks is considered risky.

Most permits can be obtained within three to six months, except for those required for the heating company, such as the exploitation plan and tariff scheme. Permission costs vary depending on the size of the project and the different permits required and can differ in different areas due to the lack of standards. Authorities' limited knowledge regarding AQE can be seen as a structural barrier. The requirement to measure water temperatures for a year before a permit can be obtained also hinders development.

Authorities for waterbodies, local initiatives, district heating companies, social housing, and energy/heating grid managing companies are all active stakeholders. AQE promotion is interlinked with the heat transition on a regional level, and local initiatives exist. For instance, the Province of Friesland collaborates with Friese Energietafel and Wetterwaarmte to develop heat grids and organise events. However, acceptance of district heating networks remains challenging due to knowledge gaps and affordability concerns leading to scepticism. More example projects could help to accelerate the process. Furthermore, the Omgevingswet (Environment and Planning Act) requires participation in any environmental change, which is a time-consuming process.

District heating networks are expected to grow over the next 5–20 years, especially in Fryslân, which has regional goals to connect 20% of buildings to collective systems, with significant emphasis on AQE systems.

To support the development of AQE, barriers can be reduced by sharing knowledge, simplifying regulations, and implementing standards. The current unclear governance structure for AQE projects, as well as the lack of AQE specific structural support, pose a barrier to AQE development. The assessment of environmental impacts, e.g. through filtration systems, needs to be facilitated in order to establish standards. In business cases for selecting a heating source, structural changes are needed to make AQE projects viable. In addition, the price gap with cheaper fossil fuels poses a significant threat to AQE technology. The planned District Heating Law (not yet adopted) could help clarify tariff structures and improve the governance of collective systems.

Additionally, a nationwide stimulation programme for AQE systems, based on the existing regional approach, could support future growth. However, it is unlikely that regulations on dike bodies will lighten, representing a barrier to AQE.

Implementing AQE on a larger scale as a sustainable heat source could help the Netherlands to achieve its climate goals. However, this would require supportive measures (e.g. tariff structure, etc.). The political weakening of the obligation for a sustainable solution in 2026 (warmtepomp verplichting – a heat pump obligation), which created a sense of urgency for consumers, has been abandoned.