BCWaterCap™

This animation shows how the pull tab seals the membrane until ready for use.  Removing the tab frees the air and liquid valves.  When liquid is sucked from the bottle, air is drawn in through the flap valve.  Once there is no vacuum pressure on the mouth piece, the air valve closes and the liquid membrane returns to a closed state.  Small arrow is air and large arrow is liquid. (click image once it has fully loaded)