I have cups too. I've never used nipples. My cups are attached to a 55 gallon water collection barrel. Went that freezes I just dump hot water in 2 big open plastic horse feed buckets and when that freezes I put the buckets on the cinder blocks with wood stumps around it for chickens to get to...
I mostly carry 1 gallon of Hot water in each hand when I go out in the morning. But for super cold temps I have an outdoor extension cord buried underground to my coop. I don't plug in a heater. I plug in a heat bulb buried in a ciderblock with a paver under and over the openings. I place my...