It is possible that the shut-off valve was blocked by the cumulated white stuff. As a result, water supply can not be stopped even when water level is high. 1 E' O0 a& A$ a2 j- O 3 a3 ?' H1 G" u! K4 k8 ^. O4 SSolution: turn off water supply and take the humidifier apart and clean it will stop the leaking. ! U; v' B8 |) ~6 F0 \! ~ U 9 e/ u G, d( M7 y * V* I# [. Q4 XOtherwise, find a professional or change a new set.