Water is going to weaken it so best to put over a treat just enough so they get the full dose. or a small bit of feed with the b complex mixed into it. You want to make sure this duckling that is having problems gets a full dose daily. I don't know why it seems just one duckling out of many will have a niacin deficiency but it seems that is usually the way it is. But there is still a good chance you can keep him from going lame in that leg if you get him started asap.