International experts recommend lower limit value for nitrate in drinking water
December 18, 2025:
An international group of experts, convened by the Danish government, has recommended that the limit value of nitrate in drinking water is to be lowered substantially. Research conducted as part of the MARCHES project has contributed to this recommendation.
Based on studies that point to a possible link between nitrate in drinking water and colorectal cancers, the Danish Ministry of the Environment in 2024 set up an international expert group tasked with evaluating the existing limit value for nitrate in drinking water according to the EU’s Drinking Water Directive (2020/2184).
The international expert group was set up in 2024 with reference to the study "Health-economic valuation of lowering nitrate standards in drinking water related to colorectal cancer in Denmark" published in Science of the Total Environment, by Brian H. Jacobsen, University of Copenhagen, Birgitte Hansen, Geological Survey of Denmark and Greenland and Jörg Schullehner, University of Aarhus – the latter of the MARCHES project.
From 50 to 6 milligrams nitrate per liter
The international expert group's report is now complete. The expert group finds that there is a small increased risk of colorectal cancer at nitrate levels well below the current limit value of 50 milligrams per liter of water. Therefore, the expert group recommends that the limit value for nitrate in drinking water is to be lowered from 50 milligrams to 6 milligrams per liter of drinking water. This recommendation is based on a precautionary approach as a protective measure against potential serious effects in the form of cancer.
The international expert group estimates that if the level of nitrate is kept below 6 milligrams per liter of water, cases of colorectal cancer in Denmark can be reduced by 57-90 cases annually.
90 percent of all drinking water supplied in Denmark contained less than 5 milligrams per liter in 2024, according to Denmark’s Ministry of Environment. However, in regions where the geological conditions do not support denitrification of surplus nitrogen from land use, public water supplies have experienced rising levels even in the deeper aquifers. The water utility of Aalborg is thus planning large-scale investment in treatment of water distributed to consumers to lower nitrate levels, that at some wells are moving towards the existing limit value of 50 mg/liter. Moreover, about 200,000 households across Denmark source drinking water from private wells in upper aquifers, highly sensitive to nitrate contamination, mostly due to excess use of fertilizers.
In connection with the publication of the report, Denmark’s Minister of the Environment, Magnus Heunicke, says that efforts are now initiated to map the precise locations with high nitrate levels and investigate what is required to lower levels in places where there are exceedances. In conjunction, efforts will continue to reduce nitrogen leaching from agricultural fertilizers, which is by far the largest source of nitrate in drinking water in Denmark.
Input from the MARCHES project
Associate professor Jörg Schullehner provided evidence to the international expert group, based on the above mentioned article and on the results obtained in the MARCHES project deliverable report: “Selected drinking water nitrate exposure-response functions with baseline incidences”. This report presents a meta-analysis of the available systematic reviews on health impacts from drinking water nitrate exposure. By revisiting these systematic reviews in conjunction with the original studies, some methodological and factual inconsistencies were detected. These were corrected in the (MARCHES) meta-analysis, showing the likelihood of health impacts well below the current EU limit value.
"I am very pleased that research conducted as part of the MARCHES project has offered what must be considered a significant contribution to the international expert group’s conclusions " says MARCHES project coordinator, Mikael Skou Andersen, Professor of environmental policy analysis, Department of Environmental Science, University of Aarhus.
The international expert group's report "Evaluation of the parametric value for Nitrate in drinking Water" can be found here: mim.dk/publikationer/2025/december/evaluation-of-the-parametric-value-for-nitrate-in-drinking-water