What happened to Scout was, I still believe, a fluke - a combination of many things that probably wouldn't have been noticed had they happened singularly, but when they all happened at once the result was his frostbitten feet. The adult chickens were never once bothered by the slight, occasional drip of the horizontal nipples we had. Any rogue drips went into the deep bedding and sank down to be absorbed slowly in the bottom layers of the litter. But Scout was tiny, and he had to stand on the bricks to reach the nipples. There is where any water puddled rather than sink down, and our temps went from a very balmy upper 60 degree day to minus 17 in the course of 26 hours. It wasn't predicted by the weather service, nor did my old hip know it was coming! We believe that standing in the water on the brick in the coop, then following Mom outside into the run was Scout's downfall.
No other chickens had any issues all winter, even during our sub-zero days and nights. We had issues with the nipples freezing a couple of times, but Ken hit them with the heat gun for a few minutes while I did morning chores, and by the time I was done the water was again flowing for the girls. I use vertical nipples for new chicks for the first few days when I brood them in their outdoor pen, and they do drip significantly more than the horizontal ones do. With the horizontal ones, sometimes water gets caught up in the tiny little cup and when temps plummet that drip freezes...followed by another the next time one of the chickens uses it. If they don't drink those little cups almost dry, the little bit of water in them freezes and so on, until there is enough ice to form icicles. The vertical nipples, however, drip every time a chicken drink, or bumps into one with her back, or bumps into the hanging waterer can even be enough to send a few more drops out of the nipple. For that reason, as soon as I see that the chicks know how to trip the mechanism, they are switched to horizontal nipples. Those just keep the area drier all the way around, I think.