I've seen cows standing around a big tub of water in a pasture, drinking away.
I had never seen one of these before yesterday.
It's clearly for the cows, and they clearly use it. I don't know how they learn to use it though. They press their noses against the balls, and press them down into their holes, into the water. They have to use a bit of force, because the balls have buoyancy and are not small. It's kind of hard to push them in. But once you push them down, there's plenty of water down in there. When you let go of them, they pop right back up into place, so the inside has to be shaped to guide the balls back into the hole.
I'm not sure what the point is. Prevent evaporation? Keep small animals and deer out? Keep it clean? The water was actually kind of dirty with cud and cow backwash in it.
How do they learn that there is water in there? The younger ones can see the older ones doing it, I'm sure, but how was that first cow trained?