Many countries expend considerable resources collecting and reporting data from national groundwater quality monitoring networks to assess diffuse nitrate contamination, but the reliability of these data depends on the effectiveness of the network. Without a representative monitoring network of reliable monitoring points, there is a risk that groundwater management policies could be developed and implemented based on poor evidence. To help increase confidence in nitrate data, a robust, practical and repeatable method was developed to assess the effectiveness of groundwater nitrate monitoring networks, and applied to a network in Scotland. The method combines a rapid site assessment of monitoring points and local pollution pressures in order to judge the reliability of monitoring points, with a wider characterization of the network to identify which land uses and hydrogeological environments are being monitored. The analysis indicates that, with minor exceptions, Scotland's groundwater nitrate monitoring network broadly represents the diversity of conditions expected in Scotland.