Nitrate in groundwater

Nitrate exceeds the limit value of 25 mg/l in groundwater at almost 15% of monitoring sites across Switzerland. In areas where arable farming is predominant, concentrations are above the limit at 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). In recent years, this limit has been exceeded at almost 15% of NAQUA National Ground Monitoring sites nationwide.

Nitrat_2022_Karte_Internet_EN_web — Nitrate in groundwater and open arable land. Data: NAQUA 2020.
© FOEN

Nitrate levels increasing again in arable areas

Elevated nitrate concentrations in groundwater are mainly due to intensive agriculture. In areas used primarily for growing arable crops or vegetables, up to 50% of monitoring sites exceed the limit value of 25 mg/l. On the Swiss Plateau concentrations are above 10 mg/l at 80% of monitoring sites.

Although there was a slight decline in nitrate concentrations until 2016/2017, concentrations have since been increasing at many monitoring sites. This increase is particularly pronounced in areas with vegetable crops and arable land, where there is a lot of excess nitrogen in the soil. In these areas, levels have increased for four years in a row.