In a study published in the scientific journal Science of the Total Environment, Brian Jacobsen, University of Copenhagen, Birgitte Hansen, GEUS, and Jörg Schullehner, Aarhus University, calculated both the benefits and costs of lowering nitrate levels in Danish drinking water. And the benefits exceed the costs of reducing nitrate levels, regardless of the method used. The study is based on results from a large population survey conducted in 2018 by Hansen and Schullehner.
In their calculations, the researchers have deducted the costs associated with reducing nitrate levels. They calculated the cost of three different solutions:
- Taking agricultural land out of production and turning it into protected areas where nitrogen is not used.
- Moving water wells away from areas where nitrate levels in drinking water exceed levels or drill deeper wells.
- Removing nitrate from the water with technologies (such as denitrification, ion exchange and reverse osmosis) that are used in other countries but are not currently used at waterworks in Denmark.
"There are advantages and disadvantages to all three solutions, and it depends on the local conditions and time horizon as to what makes the most sense. For example, setting aside agricultural land is relatively cheap, but it can take up to 50 years for the effect of groundwater protection to materialise," says Birgitte Hansen.
Drinking water analyses from GEUS' Jupiter database show that approximately 10% of Danish drinking water has a nitrate content above 9 mg/L, and another 10% is above 4 mg/L as an average for 2018-2021. Most water supplies with nitrate content at these levels are small, privately owned wells supplying fewer than nine households. But this also applies to several hundred public waterworks, especially in the area around Aalborg, as you can see in the map below.
Private wells that supply only one household have not been subject to monitoring of drinking water for nitrate since 2019, and therefore the nitrate content in these wells is unknown. Overall, approximately 4% of Danes get their drinking water from private wells. This corresponds to approximately 237,000 people.
The study is funded by Innovation Fund Denmark as part of the Mapfield project.
Read more about the study in a press release on ku.dk