Well, there's a tried and true DIY waterer for ducks that takes a gallon, or half gallon jug and puts a hole in it about chest height on the ducklings. That hole should be just big enough to let the duckling put his head in, but not so big to let him shove his body through.
This can give you...
I'll second this. They are taking to the water like, well, ducks to water. They won't have the hydrophobic oils, but they will have the ability to get under the lamp to heat up and dry off. Generally though it's recommend that swim time be limited for a few weeks.
What kind of waterer is this...