I keep a cup for measuring children's medication in mine filled with water. It still gives the turner enough room to move around. The humidity stays around 40-45 %. I have to fill it daily but it really helps with fluctuations. When it goes on lock down and the top tray gets removed I put a taller shot glass in that has more surface area and and is taller to keep chicks out. I use a sponge then as well if needed.