I am in desperate need of some help.

We just hatched 12 Mallard eggs in 2 hatches; 10 ducklings then 2 ducklings 3 weeks apart. The first 10 did great for a few days then one evening after giving them fresh water, over half died. A day later 1 more, then next day 2 more. We were down to 2 when our last 2 hatched. They were 3 weeks apart, so we kept them in 2 seperate homes. We noticed that they seemed to be dying after drinking a lot of water, almost like they wouldn't stop until it was gone.

I was determined to keep these ones alive and lilerally watered them every hour or 2 so they wouldn't over drink all while thinking-they are DUCKS!

Last night, they were all drinking for about 5 minutes when I looked in on them. One of the new babies (1 week old) were dead and they other was very wobbly. My boyfriend picked that one up and was trying to keep it awake, it seized in his hand and died.
The bigger two, who are now 1 month old, were also acting funny. One was walking like he was drunk and the other seemed ok and was trying to encourage the other to bo ok. All of a sudden the normal one fell over and looked like he was seizing.
We literally tried to do duck CPR because this guy happened to be my personal favorite, with no success. The last little guy is still doing ok.

Does ANYONE have any suggestions??? We have hatched ducks, geese and chicks before with NO problems. We use electrolyte water, both with and without probiotics, use started feed approriate for all feathered birds, not chick food. They had warming lights, clean bedding, and we did not have them swimming yet. I am at a complete loss.

Any help would be greatly appreciated!!
Thank you!