Chicks will be normally attracted to open water pans for the first 10 days, and may jump in and drown. I can’t see your setup, but it looks like a normal chick waterer in use. The problem could be with having ducklings in the same brooder. It is dangerous for the chicks to be getting wet, so I would separate them, and make sure there is plenty of room. They can be piling on and smothered if the ducks are bothering them, and they could be kept from food. Ducks need water to dip their beaks into, so it might be better to wait until the chicks are older and can get around well before having them together.
SANITARY REASONS! Never house ducklings with chicks. Ducklings are high maintenance and messy. The health of your chicks are in jeopardy as long as the are together in a close environment.Why do you recomend another box for the ducklings?
Also by placing marbles in the chicks water rim, will keep them from walking in the deep rim.