Rørcenter-anvisning 003: Rainwater Use for WC Flushing and Washing Machines
Rørcenter-anvisning 003 is the technical guideline for the collection and use of rainwater for toilet flushing and laundry in residential and office buildings in Denmark. Published by the Rørcentret at the Danish Technological Institute (Teknologisk Institut) in September 2012, this fourth edition was prepared for the Danish Nature Agency (Naturstyrelsen) and the Danish Energy Agency (Energistyrelsen). It serves as the primary reference for compliance with the Danish Building Regulations (Bygningsreglementet) and the Water Supply Act (Vandforsyningsloven) regarding secondary water systems.
The document provides technical requirements for system design, including roof surface suitability, filtration, storage tank dimensioning, and distribution. It specifically governs rainwater collected from roofs; the use of greywater, drainage water, or surface water from ground level for these purposes is not permitted under this framework. The guidelines detail mandatory safety measures, such as Type AA or Type AB air gaps to prevent the contamination of public drinking water supplies, and provide specific instructions for both new constructions and the retrofitting of existing buildings.
This guidance is intended for municipal planners, building authorities, consulting engineers, and authorized contractors in the plumbing and sewerage sectors. It defines the administrative procedures for permits and the technical standards required for the legal installation and maintenance of rainwater harvesting systems.
Scope and Permissible Applications
The use of rainwater is categorized based on the building type and the level of public access. Under Bekendtgørelse nr. 1024, specific restrictions apply to sensitive populations.
- Existing single-family houses: Permitted without formal application to authorities.
- New houses and apartment blocks: Permitted following a successful application to the municipality.
- Public institutions (schools, offices, libraries): Rainwater may be used for WC-skyl (toilet flushing) but not for tøjvask (laundry).
- Prohibited locations: Rainwater systems are not allowed in hospitals, nursing homes, or childcare centers for children under six years of age (e.g., nurseries and kindergartens).
Technical System Components
A compliant system must follow the principles of collection, filtration, and storage to ensure water quality and system longevity.
- Collection Surfaces: Only suitable roof materials like clay tiles, concrete, or slate should be used. New bitumen, grass, or copper roofs are considered unsuitable due to discoloration or metal leaching.
- Filtration: Systems must include a filter with a mesh size between 0.18 mm and 0.5 mm. Common types include vertical downpipe filters, Cyklonfilter (cyclone filters), and inclined filters.
- Storage Tanks: Tanks can be placed in basements or buried. To limit bacterial growth and Legionella risk, the temperature in the tank should not exceed 18 °C.
- Inlet and Outlet: Tanks must feature a beroliget tilløb (calmed inlet) to prevent sediment disturbance and an overflow with a 20-45° angled cut to remove floating debris.
Protection of Drinking Water Supplies
The most critical safety requirement is the prevention of backflow into the public water network. Direct connections between rainwater pipes and drinking water pipes are strictly prohibited.
- Air Gaps: Topping up the system with drinking water during dry periods must occur via a frit luftgab (free air gap) of Type AA or Type AB.
- Backflow Protection: A Type BA backflow preventer must be installed at the building's main water entry point.
- Labeling: All rainwater pipes and outlets must be clearly marked with labels such as Regnvand - ikke drikkevand (Rainwater - not drinking water) to prevent accidental cross-connections.
Authorization and Maintenance
Installation and maintenance are regulated by the Autorisationsloven. Owners are responsible for ensuring work is performed by qualified professionals.
- Authorized Sewer Contractors: Required for all underground work, including tank installation and drainage pipes.
- Authorized Plumbing (VVS) Contractors: Required for all internal water installations from the pump to the tap points.
- Inspection Intervals: Filters should be cleaned 2-4 times annually. Pumps and backflow preventers require annual inspections. Storage tanks should be inspected for sediment every 10 years.
Frequently Asked Questions
Can I use rainwater from a copper roof for laundry?
No, copper roofs and gutters are unsuitable as the metal content in the water can double over time and potentially cause staining or corrosion.
What is the maximum allowed temperature for stored rainwater?
The water temperature in the storage tank should ideally not exceed 16–18 °C to minimize the risk of bacterial growth and Legionella.
Is it legal to install a tap on a rainwater system?
No, it is strictly forbidden to install taps (faucets) on a rainwater system, either indoors or outdoors, to prevent accidental consumption of non-potable water.
How often must the rainwater filter be cleaned?
Rainwater filters should generally be cleaned 2 to 4 times per year to maintain efficiency and hygiene.
Does the system require a water meter?
Yes, many municipalities require a water meter to measure the used rainwater if the property owner is to receive a reduction in the wastewater discharge fee (vandafledningsbidrag).
Which backflow prevention type is required for drinking water top-up?
The system must use a type AA or AB backflow protection with a free air gap of at least 20 mm or twice the internal diameter of the inlet pipe.
