Case

Rainwater for washing machines and toilets cut water consumption by 40 percent

Up to 10,000 households’ washing machines and toilets in the suburb Nye – near the city of Aarhus - will soon use rainwater instead of drinking water. This is estimated to cut water consumption by as much as 40 percent.

Water resources worldwide are under strain. New solutions need to be tested and implemented to ensure that the next generation has better access to water. However, in the developed world water is being consumed indiscriminately. Therefore, in the newly constructed district Nye, which is a suburb of the city of Aarhus, rainwater will be used for toilet flushing and laundry. Up to 10,000 homes are planned to be built in the new district.

Most commonly in the developed world, we are washing our clothes and flushing our toilets with clean drinking water. However, using rainwater instead could cut drinking water consumption by as much as 40 percent. It can also create a clear division between the essential drinking water and water used in everyday chores.

Purple pipes, an artificial lake and UV-disinfection

In Aarhus Vand we have developed a solution where rainwater will be used for toilet flushing and laundry – in collaboration with Tækker, COWI, and Silhorko. The solution could be a vital part in the development of new sustainable districts throughout the world.

We take the rainwater, which is collected in a lake that we have built and clean it at the treatment plant. The treatment is done by a special ultrafilter and ultraviolet disinfection system, among other methods. We then send the water out into the homes via a separate pipe system we have developed for this purpose. The pipes are sized based on a calculation of the need for water for laundry and toilet flushing, and they are colored purple so that they are clearly different from the drinking water pipes. This will minimise the risk of malfunctioning.

The solution will also work in case of droughts. When there is insufficient rainwater available, the water supply is supplemented with wastewater from drains, which is also treated at the treatment plant. The entire infrastructure to direct the purified rainwater out to the residents of Nye has already been established. The purification plant itself is ready by the end of 2020.

Extreme rainfall and flood proof district

In addition to handling everyday rainfall, the district also deals with a rising threat of extreme rainfall due to climate change. Roads and paths are constructed to function as waterways, which should reduce the need for larger sewage pipes or delay pools during heavy rain.

By using roads, paths and green areas to direct the water where it does the least damage, we handle extreme rain intelligently. We must not rely solely on laying pipes to alleviate extreme rain. For example, roads direct the water to ball courts and parking lots designed to handle water in extreme quantities. Thereby, the solution combines water management with livability by using recreational spaces as flood protection.

Why is the project interesting?

  • It challenges current legislation
  • It challenges common practice
  • It demonstrates holistic water management in a large area
  • It is a new, untested solution that is being developed ad hoc
  • It involves cooperation between all involved parties
  • It is a full-scale demonstration
  • It may prepare the ground for a new land development practice

Project scope

The project involves rainwater collected from roofs, roads, etc. to be used for toilet flushing and laundry. This reduces the consumption of drinking water by approx. 40%.

The production of secondary water takes place centrally, and the entire solution is managed by professionals.

The solution is designed to minimise the risk of incorrect connections.

The residents assume no operational responsibility; nor should they have to want for anything – despite the sustainable lifestyle.

The project demonstrates how it is possible to create innovative solutions in new land development when all parties strive to succeed.

Watch video presentation (Danish speak)

About author

As one of the most innovative water companies in Denmark, we feel obliged to support the water industry. We have extensive knowledge of the operation of various facilities, establishment of organisations, analysis, tendering, planning, project management, training and commissioning of facilities. We would like to do our share towards ensuring innovation of the Danish water industry. By also taking a global perspective, we contribute knowledge and support for Danish exports and help set the global agenda for sustainable development.

Primary contact
Flemming Fogh Pedersen

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