Nitrate in groundwater
Nitrate exceeds the limit value of 25 mg/l in groundwater at around one in six monitoring sites across Switzerland. In areas where arable farming is predominant, concentrations are above the limit at more than 50% of monitoring sites.
Groundwater contains very little nitrate naturally. For groundwater used for drinking water or intended for such use, the Waters Protection Ordinance (WPO) prescribes a limit value ('numerical requirement') of 25 milligrams per litre (mg/l). Over the past ten years, this limit has been exceeded at up to 18% of NAQUA National Groundwater Monitoring sites nationwide.
The limit value is frequently exceeded in arable farming areas
Elevated nitrate concentrations in groundwater are mainly due to intensive agriculture. In areas used primarily for growing arable crops or vegetables, more than 50% of monitoring sites exceed the limit value of 25 mg/l. On the Swiss Plateau concentrations are above 10 mg/l at around 80% of monitoring sites.
Following a slight decline of the number of monitoring sites exceeding the limit value in groundwater during several years, this number has increased again since 2017. This increase was particularly pronounced in areas with vegetable crops and arable land, where there is a lot of excess nitrogen in the soil.
Both hydrological and various agronomic factors are possible drivers of increased nitrate concentrations under cropland. Clarifications are underway.
Indicator Nitrate in groundwater