Something I've discovered with the cool-mist Humidifiers:
**don't over-tighten the "cover"...it's more prone to leakage that way.
Yes, I've still had some that leaked, but that was one of the big issues I had anyway.
There's one that Sunbeam makes and there's a "generic" type sometimes of it at Walgreens - it has a blue nightlight that shines up through the tank. We have one in my daughters room and one in ours. Our daughters really like it and it's sort of "dual purpose" in that you don't need an additional night light.
We have had the same issue with leakage with it on occasion, and it was usually me over-tightening the lid to the tank.
For what it's worth, and good luck!