First appeared in


100 climate solutions from Danish Municipalities


In Aarhus Municipality, a holistic approach to water management is having a positive impact on the way people think about “waste” water.

Throughout much of Denmark, local rainwater drainage systems have been used in new urban developments as a flood defense measure, but rarely has this same water then been cleaned and reused afterwards. This is exactly what is happening in Aarhus. A collaboration between the municipality, the water utility and an engineering firm has led to a central non-potable water store, where rainwater is collected, purified and redistributed for local use. The centralized water store has the capacity to handle a 1-in-10-year rain event, and incorporating the grey-water storage in the connected building raises this to a 1-in-100-year rain event.


In practice, rainwater is collected in streams and is led through smaller lakes
to a central collection reservoir. A filter removes particles and keeps plants and animals out, before water is moved from the reservoir to the treatment plant. From there, the purified water is distributed to people’s homes where it is used for flushing toilets and doing laundry. The local “waste” water now covers 40% of water consumption in the area. An important part of the project is to establish quality standards for non-potable water used for toilets and laundry. Aarhus Municipality has played a central role in ensuring that there is no risk to citizens’ health.

The project demonstrates that “waste” water can become a new resource that reduces demand for groundwater.

How the Global Goals are addressed

Clean Water and Sanitation

Although Aarhus is not a water-stressed city, protecting groundwater reserves by reusing rainwater shows commitment to responsible water management.

Responsible Consumption and Production

The solution helps citizens take care of their clothes: non-potable water is not as hard as groundwater, which can reduce the need for soap and increase the life of washing machines.

Life Below Water

The collection reservoir has become a natural and recreational feature of the urban landscape in the city of Aarhus, as well as a place where plants and animals can thrive.