7. All water used in the watertightness tests is recycled. Ten cubic metres of water drawn from a sump tank circulate in the test room’s closed circuit. “We recycle up to 375 litres per minute and, when running at high speed, up to 1,000 m3 per month,” explains Pavel Novotný, another member of the team. During cleaning, the water passes through coarse and fine filters and is disinfected with UV radiation every night. The water in the circuit is changed once a month and then flows into the sewer.