After years of operating on the International Space Station there are tiny holes in that water separator that eventually got clogged up due to tiny particles of contamination in the water. The end result is that the water had to go somewhere and it "carried over" into the air system. read more
You are probably seeing videos of astronauts in the water and not in space. There are 2 large underwater training facilities. The NBL (Neutral Buoyancy Lab) near the Johnson Space Center in Houston Texas, and the large pool at the Yuri Gagaran Cosmonaut Training Center in Star City, Russia. read more