You can use a sponge and wet it. It depends how much water you want on what you're trying to keep your humidity percentage at. Put a wet sponge and see how high it goes, if it's too high then squeeze some water out. If it's low, add another sponge with water. Have a container full of water without a barrier can be a risk for the chicks to drown as they don't know how to walk right after hatching.