How would hens with small combs all be getting the tops of their heads wet, from drinking from a container? Mine dip their beak in the water, not their entire head, when they drink. I could understand one freak accident, but not as a normal flock occurrence. Chickens drink water in areas with harsh winters every year, without a problem. If they were talking about roosters from breeds with large pendulous wattles drinking out of deep containers, having a problem with their wattles, maybe. Small combs on hens? That just sounds odd to me.
More likely, it's a problem with wintertime coop air management, which can cause frostbite. Either chickens that are in air that's freezing, but too humid, due to inadequate ventilation or chickens in a freezing coop that are roosting in a draft.
Forcing birds to eat snow to survive just chills their core body temperature more. They can survive that way, but it just makes harsh weather even harder on them.
We've used big galvanized poultry waterers on metal heated bases, heated dog bowls, stock tanks with floating heaters and submersible heaters. They've all worked for us. The most important thing to me is to set them up as safely as possible. Secure things so that they can't be tipped over and have a heating element come in contact with flammable bedding. I like anything in the coop to be elevated on a fireproof base. We've never had a problem, but it always pays to think about what could happen if something electrical, that's encased in plastic, went "wrong." Isolating heating elements from coop litter is just good common sense.
