In contrast to nitrogen in groundwater (where a unified threshold is defined for all groundwater bodies in Europe), for surface water the Water Framework Directive requires the establishment of type-specific reference conditions for surface water body types. The Water Franmework Directive thus proposes to define type-specific conditions for these reference values which may be either spatially based or based on modelling, or may be derived using a combination of these methods. Where it is not possible to use these methods, Member States may use expert judgement to establish such conditions. Good surface water status means the status achieved by a surface water body when both its ecological status and its chemical status are at least good (EU/WFD 2000).
A driving force indicating nitrates in surface waters is the susceptibility to erosion and compaction.