How can I lower the humidity level in my leopard gecko's cage?

My leo’s cage is a 20 gallon. I have the water on the cool side of the cage but the humidity level is over 50% almost all the time! So far, it doesn’t seem to have effected him at all, but I want to be safe. All that’s in there:
cool side: food dish, hideout, water bowl, climbing vine.
hot side: rock for basking, fake cactus.
The substrate is white sand( it never gets wet). His cage has a wire mesh covering. I don’t know how or if this will help, but I want to get the best answer possible.
How can I lower the humidity level? Possibly without drilling holes or something like that?