Nitrate exceeds the limit value of 25 mg/l in groundwater at almost 15 % of the monitoring sites across Switzerland. In areas where arable farming is predominant, concentrations are above the limit at more than 40% of the monitoring sites.
Groundwater naturally contains very little nitrate. For groundwater that is used for drinking water or is intended as such, 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 12% to 15% of the NAQUA monitoring sites nationwide.
Elevated nitrate concentrations in groundwater are mainly due to intensive agriculture. In areas used primarily for growing arable crops or vegetables, more than 40% of monitoring sites have exceeded the limit value of 25 mg/l in recent years. Mostly affected is the Swiss Plateau, with concentrations above 10 mg/l at 80% of the monitoring sites.
