The borosilicate glass mouthpiece offers the best combination of strength and clarity and has been designed to curve to the perfect angle for exceptional comfort and cleaning convenience. It can be easily attached to the mouthpiece with a delicate magnet placed inside the mouthpiece. The magnet of the mouthpiece has been treated with a state-of-the-art rust prevention process and to complete the Hydrology9 portable liquid filtration experience, a ball valve has been perfectly positioned inside the mouthpiece. Thanks to gravity, air can easily rise and the liquid will not spill if it is turned over. This design allows the Hydrology9 to be carried and turned in any direction without fear of tipping over.