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 f9 w* T6 Y# n k2 ~$ q @! J+ L3 U 6 {! K. r+ J- J3 KSolution: turn off water supply and take the humidifier apart and clean it will stop the leaking. $ |7 y* g3 n, W- @8 _! g 1 D8 p. n! Y( [ X0 U8 v- f: S / [9 j! `+ j/ n: @Otherwise, find a professional or change a new set.