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. 2 i' }$ i: M4 H$ y
6 v( z6 y0 d9 \2 y* G9 r: M8 q
Solution: turn off water supply and take the humidifier apart and clean it will stop the leaking. 5 t% Z8 T8 \$ m( l A- E 4 y- s, U; y: v3 [ `2 @9 d" t3 |6 q4 ]9 S
Otherwise, find a professional or change a new set.