You know, I have a sponge in a large soap dish in my bator, but the recommendation from most professional sites say that the area of the water should be about 1/2 the area of the incubator. When I candle next I'm going to take the sponge out for just the same reason as you mentioned. Also, I have a homemade Miss Prissy 'bator and I started squirting water with a syringe (you could use a turkey basting syringe) into the bottom of the bator (the wire, etc. is about 2 inches above) and since doing that I've had NO problem keeping my humidity exactly where it needs to be. When it drops below about 47% I add a couple more syringes of water in the bottom.