All repeated information already, but thought I'd share a previous comment I made about our water method during winter. The post itself also has great suggestions like this thread does https://rabbittalk.com/threads/winter-water.34402/post-334997
I wonder if you can also buy heated "tape" (more of a strip) and try finagling it around each of the bottles near the nipple but outside of the cage. If your nipples are freezing, that would certainly help, but I don't know what temp it brings it to or if it's regulated. They are designed to wrap around pipes and keep your house water from freezing in the pipes. They're likely a safe temperature, but do check first. Would hate to have burnt bunny tongues!
Just a thought!
I wonder if you can also buy heated "tape" (more of a strip) and try finagling it around each of the bottles near the nipple but outside of the cage. If your nipples are freezing, that would certainly help, but I don't know what temp it brings it to or if it's regulated. They are designed to wrap around pipes and keep your house water from freezing in the pipes. They're likely a safe temperature, but do check first. Would hate to have burnt bunny tongues!
Just a thought!