I believe the question was, "how can I ensure that my gecko stays hydrated?" not, "can anyone notice if their gecko drinks water, and if they can, is it just because of evaporation?"
I have found that if I regularly mist their humid hides, if the geckos don't drink directly from their water bowls they will at least lick the beads of water from misting. They are essentially desert reptiles, so they don't need a lot of water.
The answer to your question, I believe, is that you need to regularly provide clean water in a dish and also provide a nicely moist humid hide. The rest, as they say, is up to the gecko.