Do not fill the Q-Cup all the way to the top. There is a water line that is about 2 about 3cm from the top of the Q-Cup. Do not fill over that line.

The Q-Cup was designed to hold some pressure and has a pressure release on the cap to prevent too much pressure when generating hydrogen. If you want to produce more hydrogen you can run the process more than once but make sure to let out some of the pressure by opening the lid first and then closing it again before generating more hydrogen in the water.