German concept for the assessment of chemicals and preparations with respect to their hazardous potential against water and organisms living in water. This assessment is determined in the VwVws ([German] “Verwaltungsvorschrift wassergefährdender Stoffe” = Administrative Regulation on the Classification of Substances hazardous to waters into Water Hazard Classes). Due to the physico-chemical properties and the toxicity, substances are distinguished into different water hazard classes (WGK = [German] “Wassergefährdungsklasse”). Preparations are distinguished following the “mixture rules” of the regulation. The following classes exist:

WGK Denomination Examples
NWG non-hazardous to water native ester oils, certain synthetic esters
WGK 1 slightly hazardous to water some acids and bases, ethanol, methanol, most of the mineral oils
WGK 2 hazardous to water light heating oil, diesel fuel
WGK 3 severely hazardous to water benzine, waste oil, halogenated solvents, chromates, cyanides