What is WILMA?
WILMA (Waterschap Informatie & Logisch Model Architectuur, roughly “Water Board Information & Logical Model Architecture”) is the reference architecture of the Dutch regional water authorities: a shared model of principles, business functions, data, applications and infrastructure that water authorities use to build their own enterprise architecture. Het Waterschapshuis, the coordinating and delivery organisation of the 21 water authorities, maintains WILMA and publishes the model online. Suppliers use WILMA as a design starting point for solutions they deliver to water authorities.
WILMA is the sectoral offspring of NORA: whatever NORA and GEMMA already cover, WILMA inherits, and only topics specific to water authorities are worked out separately.
🎯 Why do water authorities need their own reference architecture?
Water authorities (waterschappen) have tasks that no other tier of Dutch government has in quite the same way: water level management, flood defences, wastewater treatment and their own tax collection. Their information provision also spans two worlds: office automation (IT) and process automation (OT) at pumping stations, weirs and treatment plants. According to Het Waterschapshuis, WILMA has four aims:
| Aim | What it means in practice |
|---|---|
| One language and better decision-making | One vocabulary for business functions, objects and components, so 21 water authorities understand each other’s diagrams and see the consequences of a choice |
| Steering towards shared strategic goals | National programmes such as the Environment and Planning Act are worked into every water authority’s architecture in the same way |
| Raising architecture maturity | Water authorities with a small architecture function do not have to start from scratch |
| More efficient information provision and services | Reusing reference components and shared services stops each water authority from reinventing the wheel |
That maturity is also measured: in 2019 and 2020 Het Waterschapshuis commissioned a national picture of architecture maturity based on the DYA maturity matrix, and every water authority took part in 2020.
🧱 How is WILMA structured?
WILMA consists of a base architecture and a series of theme architectures. The base architecture starts from the foundations and then follows the layers you also find in ArchiMate:
| Component | Content |
|---|---|
| Foundations | Legislation, basic principles and derived principles |
| Organisation | Products and services, business functions, sub-functions and business processes (business architecture) |
| Information | Business objects and standards (information architecture) |
| Application | Reference components plus national and sector-wide services (application architecture) |
| Infrastructure | Generic technical facilities (technical architecture) |
The theme architectures go deeper into topics that cut across those layers, such as information security, the Environment and Planning Act (Omgevingswet), the Single Digital Gateway, the Open Government Act (Woo), asset management, data management and managed services.
Which basic principles does WILMA use?
The nine basic principles (BP01–BP09) are based on the NORA principles and partly taken from GEMMA. They are phrased as “Our water authority …”: it gives the customer a good information position, thinks from the customer’s point of view, digitises its services and processes, handles data confidentially, uses generic processes and functions, collaborates, works securely, is future-oriented and spends public money efficiently. From these, derived principles are formulated that are concrete enough to test a project design against.
🏭 Which business functions does WILMA distinguish?
The business function model is the heart of WILMA. It divides a water authority into three groups: governing functions (strategy and steering, policy and architecture, organisation management, change management), supporting functions (such as financial management, information management, IT management and procurement) and primary functions. It is precisely the primary functions that rely on OT:
| Primary business function | Typical OT and data |
|---|---|
| Water system management | Pumping stations, weirs, inlets and level measurements, controlled via PLCs and RTUs |
| Water chain management | Wastewater treatment plants and sewage pumping stations with SCADA, telemetry and a historian |
| Flood defence management | Inspection and monitoring data for dykes and hydraulic structures |
| Emergency management | High-water and incident information, linked to process displays and monitoring networks |
| Waterway and road network management | Movable bridges, locks and road management systems, depending on the water authority |
| Data management | Management of measurement and object data according to sector standards |
WILMA also lists relationship management, regulation and incentives, tax collection and flora and fauna management among the primary functions.
🌊 How does WILMA help with IT/OT convergence?
WILMA is not an OT standard, but it gives OT a place in the bigger picture. In WILMA, a pumping station is at the same time an asset in the asset register, a source of measurement data and an object in the information architecture. Modelling that unambiguously lets you link process data from SCADA reliably to asset management, lifecycle management and reporting, instead of building a one-off interface for each project.
For the data itself, the sector relies on its own standards:
- Aquo - the Informatiehuis Water standard for exchanging data on surface and groundwater management and wastewater treatment; on the Dutch Standardisation Forum’s ‘comply or explain’ list since 2010 (current version Aquo 2026-06)
- DAMO (Data Afspraken Modelmatig Ondersteund) - the logical data model for objects such as watercourses, hydraulic structures and flood defences, maintained by Het Waterschapshuis together with Informatiehuis Water
A water safety elaboration from the 2016 ‘WILMA op de kaart’ project, for example, built on DAMO Keringen and its central distribution layer. The models are recorded in ArchiMate.
🔐 How does WILMA relate to security and compliance?
In WILMA, information security is a business function in its own right: a coherent set of measures for the availability, integrity and confidentiality of information and information systems, including CIA classification, authorisation and DPIAs. The “works securely” principle makes security by design the starting point for every design.
The concrete compliance requirements come from outside WILMA:
- BIO - the Government Information Security Baseline; BIO2 has been mandatory for public bodies in scope of the Cybersecurity Act since that act entered into force on 15 August 2026
- CSIR - the Cybersecurity Implementation Guideline for Objects (Cybersecurity Implementatierichtlijn Objecten) from Rijkswaterstaat and Het Waterschapshuis, covering the process automation of pumping stations, locks and treatment plants, based on the BIO and IEC 62443
- CERT-WM - the water authorities’ cybersecurity team since 2016 and their designated CSIRT under the Cybersecurity Act
WILMA makes sure these requirements have a fixed place in the architecture, for example through network segmentation between office and process networks in the infrastructure layer. See also Water Sector OT Security and the wider topic of OT security.
🔧 How does a water authority use WILMA in a project?
A practical approach for an architect or project manager, for example when replacing a telemetry system:
- Position the question - which business function is supported (here: water system or water chain management) and which processes are affected?
- Test against the principles - which derived principles apply, for example on reusing generic components and working securely?
- Choose reference components - is there already a national or sector-wide service, or a component other water authorities use?
- Define the data - which business objects are involved, and are they exchanged according to Aquo and DAMO?
- Secure the design - classify for confidentiality, integrity and availability, apply the CSIR to the OT part and place the system in the right network zone.
- Record the design - in ArchiMate, so your own architecture model stays aligned with WILMA.
🔗 How does WILMA relate to other Dutch government architectures?
| Architecture | Tier of government | Relationship with WILMA |
|---|---|---|
| NORA | Whole of government | Parent architecture; WILMA principles are based on it |
| GEMMA | Municipalities | Sister architecture; WILMA reuses GEMMA content under “NORA/GEMMA unless” |
| MARIJ | Central government | Sister architecture, relevant when working with Rijkswaterstaat |
| PETRA | Provinces | Sister architecture, relevant for area-based collaboration |
❓ Frequently asked questions
What does the abbreviation WILMA stand for?
WILMA stands for Waterschap Informatie & Logisch Model Architectuur, roughly “Water Board Information & Logical Model Architecture”. It is the reference architecture of the Dutch water authorities and is maintained by Het Waterschapshuis.
Is WILMA mandatory for water authorities?
WILMA is a reference framework, not a legal standard. Water authorities use it as the basis for their own enterprise architecture; obligations such as the BIO and the ‘comply or explain’ list for standards like Aquo come from other frameworks.
What is the difference between WILMA and NORA?
NORA is the reference architecture for the whole of Dutch government. WILMA is the sectoral elaboration for water authorities: it inherits NORA and GEMMA content and only works out topics specific to water authorities, such as flood defence management and tax collection.
Does WILMA contain requirements for OT security?
WILMA includes information security as a business function and the principle that the water authority works securely, but no detailed OT controls. Those are in the CSIR, which is based on the BIO and IEC 62443.
Who can use WILMA?
WILMA is primarily intended for architects and information managers at the 21 water authorities. Suppliers can use WILMA as a design starting point for products and services for water authorities.
How is WILMA maintained?
Het Waterschapshuis maintains WILMA with a dedicated WILMA team and publishes the model online. Communities of water authority representatives work with that team to develop the theme architectures.
📌 In summary
WILMA is the reference architecture that gives the 21 Dutch water authorities one language for their information provision, from tax collection to pumping station. Based on NORA and GEMMA, WILMA adds a business function model, nine basic principles and theme architectures. For OT, it provides the framework on which sector standards such as Aquo and DAMO and security frameworks such as the BIO and the CSIR are hung.