These include solvents, mixtures containing mineral oil (diesel fuel, gasoline, etc.), residues containing mineral oil (waste oils), plant treatment agents, heavy metals (e.g. cadmium, mercury), halogenated hydrocarbons, acids, alkalis, PCBs, etc.

Substances hazardous to water are divided into 3 water hazard classes (WGK) depending on their hazard potential:

WGK 1 = slightly hazardous to water (e.g. coolant)
WGK 2 = hazardous to water (e.g. heating oil, diesel fuel)
WGK 3 = highly hazardous to water (e.g. waste oil)

The range of system types extends from the public filling station or chemical storage facility of an industrial company to the privately used heating oil tank in the basement of a detached house. There are also facilities for the storage of liquid manure, slurry, silage slurry and manure in agriculture.

Special technical requirements must be met when storing, transferring, producing or using these substances.

According § 40 of the Plant Ordinance (AwSV), the installation, assembly, maintenance, operation and significant modification of systems for handling substances hazardous to water must be reported to the lower water authority at least 6 weeks before the start of construction or the intended action.