If this was water you would be sick.
Add rocks to water to keep them from guzzling. I use chicken waterers for first 6 weeks and then let them have a pool.
Waterfowl do not need medicated feed and although they can be given medicated feed their first 2 weeks of life, after that it should be non-medicated because some ducks can be highly sensitive to amprolium. Waterfowl rarely ever get coccidiosis so why feed and tax their systems. Also, David...
Is your chick starter medicated? You have to have unmedicated for waterfowl.
And your using prime to sort of leech out what your area is putting in water to kill something in their water system? If so why not buy bottled water until they are done?