I don't think that waterer is deep enough for them to be able to submerge their heads.If you haven't already, I'd put the waterer on top of a grate in a tray. Like this: https://ecetohomesteading.com/how-to-make-a-no-mess-duck-brooder/
I think that specific one should be okay for a few weeks, but then they’ll definitely need something deeper, yeah.
Yeah, I noticed that too. The feeder also seems a little small, yeah? I've never raised small ducklings in a brooder.
Very small. Their heads grow very rapidly as well. My ducks are just over 8 weeks and are full size and feathered. It's fast. I upsized their water weekly. That water isn't deep enough.
The author of that article wrote, "When the ducklings were very small I used a chicken feeder filled with water. It allowed them to put their beaks in and drink the water and it was deep enough for them to dip their entire beak to clean their nostrils. When they got bigger I moved to a 4L milk jug with two large holes cut for them to be able to dunk their heads."
ah ok! I have one of these chick feeders as their waterer right now so they can stick their head in but not swim in it. How long do you think before I'll have to get a new one?
the only surface in the garage was this decade old freezer 
I wouldn’t be concerned just yet. There’s a lot of things that can affect weight. If she’s gaining weight and seems happy and healthy, most likely she’s alright.
Yep, they’re little pooping machines. I’ve never washed so many clothes and towels
