The results presented here are an experimental investigation of single phase and two-phase flow of water through pin holes and defined slits. The project was performed to extend the database of experimentally determined leak rates at thin-walled components. Test specimens described herein include five pin holes and three different geometries with defined slits and were manufactured with a wall thickness t of approximately 1.2 mm. Leak rate measurement was performed in parameter range with temperatures ranging from 20 °C to 230 °C and a pressure range from 5 to 75 bar. These experiments cover a t/dh ratio range from 1.4 to 12. Furthermore, leak rates with discharge into a water vessel are compared to free discharge into air environment or rather approximately free discharge into a condenser. As a part of these investigations the formation of a metastable fluid phase in the flow regime at the outlet of the apertures was documented with a high-speed camera, evaluated and categorized for different geometries. Within this contribution an overview of the test facility, the testing procedure, and a selection of results of the investigations will be presented and discussed.