Take a look at tweetysvoice and 70%cocoa's setups for water management. Just want you to know that almost all of us, from what I read here, struggle at first with water management. You can get it sorted out and life will be better.
But the answer is not to reduce ducklings' access to water. No, they need water for drinking and head washing at a minimum. And 24/7 for, IMO, the first ten weeks. Then only eight hours at a time without water, and never any food without drinking water.
Regarding the neck problem, I would put triple antibiotic ointment (no pain killer - that's toxic) on the neck, just a tiny dab, twice a day for four days. It is irritated, and I would hate to see it infected.
Now there's always the possibility of a fungal infection, so keep watching it. If it looks fungal, you'd want a different kind of salve.
Watch that heat! People have overheated their ducklings to the point of death, sadly enough. I kept a small thermometer in the brooder, and always there was room for the ducklings to get away from so much heat without getting chilled.

But the answer is not to reduce ducklings' access to water. No, they need water for drinking and head washing at a minimum. And 24/7 for, IMO, the first ten weeks. Then only eight hours at a time without water, and never any food without drinking water.
Regarding the neck problem, I would put triple antibiotic ointment (no pain killer - that's toxic) on the neck, just a tiny dab, twice a day for four days. It is irritated, and I would hate to see it infected.
Now there's always the possibility of a fungal infection, so keep watching it. If it looks fungal, you'd want a different kind of salve.
Watch that heat! People have overheated their ducklings to the point of death, sadly enough. I kept a small thermometer in the brooder, and always there was room for the ducklings to get away from so much heat without getting chilled.