Purified rainwater for toilet flushing and laundering

In the district of Nye, north of Aarhus, sustainability is paramount. The city district is designed to utilize water as a resource. The increasing volumes of water resulting from climate change are therefore included in the district as recreational elements like lakes and canals.

To save on the precious groundwater resources, a new method has been developed to utilize and purify rainwater and drainage water in the area so that the water can be used for toilet flushing and laundering. Secondary water covers as much as 40 % of the area's water consumption. Though secondary water is not of drinking water quality, it can be used for secondary purposes.

The water treatment plant is designed to handle fluctuating raw water quality. Changing seasons and the amount of precipitation affect the quality composition of the raw water, which in contrast to groundwater is not static.

The secondary water undergoes three treatment steps: Pressure filtration with filter media consisting of several types of gravel and anthracite, ultrafiltration for removal of particles down to 0.02 micrometres, and finally treatment with ultraviolet light (UV) to decompose microbiological growth.