I have ducklings inside the house currently, well it's warm enough in their brooder that a heat lamp isn't needed, so this year I have been turning the heat lamp off at night, so it's completely dark and the ducklings can't see so they are unable to drink or eat.
I actually prefer doing this since it more replicates how ducklings in the wild would be at night. Under their mother without feed or water. I think doing this helps prevent leg problems in heavyweight breeds thus affecting their overall growth rate. I think ducklings that are under heat lamps 24/7 grow to fast and end up with more problems compared to one's in a more natural setting.
Everyone has there own way of doing everything, but I do disagree that they NEED food/water 24/7.