Installations for handling substances hazardous to water (e.g. heating oil consumer installations, filling stations, ...) must be notified to the responsible water authority and inspected by an expert body, depending on their hazard potential, their location (above ground, underground) and their location in a protected area (water or medicinal spring protection area, floodplain). The legal basis for this is the Plant Ordinance (VAwS).

For example, above-ground heating oil consumer systems with a storage volume of more than 1 m³ must be inspected prior to commissioning and, in the protected area, periodically and when decommissioned; underground heating oil consumer systems must be inspected prior to commissioning, periodically and when decommissioned. Installations in which other substances hazardous to water are stored are subject to staggered inspection obligations, depending on the hazard level.

The inspections are carried out by expert bodies in accordance with § 22 VAwS and monitored by the responsible water authorities.
Expert bodies may act in accordance with the scope of their approval. Approvals may be limited to certain inspection areas or be limited in time. Approvals from other federal states are also valid in Hesse.

Approvals from other member states of the European Union, a contracting state of the Agreement on the European Economic Area or Switzerland shall be deemed to be an approval if their equivalence has been determined by the approval authority and published in the State Gazette for the State of Hesse.