The mineral content of your water is too high. This will cause the water to boil too vigorously and percolate up through the hole. Try mixing about 75% distilled water in with the water you are currently using. Don't use 100% distilled water because that won't work at all.
The soft silicone gasket that fits around the container and base of the water reservoir must be dry, flat in place, and even all around to make a good seal. The unit must be LEVEL and not crooked or leaning in any one direction. If you have a leak, other than the gasket is a defect of the molded case or parts. If its within the warranty terms, return it for a replacement.
Not sure what make or model you have but if it's a auto -fill shut off the auto fill and see if the water level goes down.
It also may not be the right size for the area/sq footage you're trying to humidify.
Make and model would help for specs of the unit.
Thanks.
The water source (tank or bottle) sits tight on the platform and there is a plastic form known as a seal to prevent leakage. You need to replace the seal.