The water dish we've been using was one of those big, shallow, rock-formation type you see in pet stores. Alas, it has a tiny crack somewhere because there's a slow leak, so we replaced it yesterday with one slightly smaller than the diameter of a CD.

Today I'm noticing after a constant humidity range of 68-72%, it dropped to 65% these past 24 hours. Sharp, instant difference! So if any of you are having a hard time keeping your humidity up, perhaps a greater surface area of water will be a big help.