I'm assuming you have a conventional glass vivarium with a sliding screen top.
If you've got an under-tank heater attached to the enclosure you don't want to pour water in that will go through the substrate directly onto the glass. This may result in cracking the glass bottom. Also watering substrate in that manner will possibly make it soggy, which you want to avoid, as too damp a substrate can cause problems with scale rot. If you aren't already partially covering the screen top with something like plastic sheeting, try doing so and see if it raises the humidity a bit. You don't need to typically cover the top completely, allowing for some ventilation. Doing that and misting lightly once or twice a day should be sufficient.
Steve
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Nature - the original Master Planned Community!