Most of the time not. Usually just being in contact with the melted water at the bottom keeps the whole thing melted. Sometimes the very top surface of the water would freeze and stick up there while the rest of the water continued to get drank. And if it gets really cold enough, there can be a whole block of ice up in there, but I don't remember it happening enough times that it was a problem. With that size waterer, it needed to be refilled once every day or two anyway, so I think it worked out to just needing refilling a little sooner when it froze up. I've been surprised at how well the reservoir stays melted. It basically doubles the capacity of the blue bowl, which I sometimes use without the reservoir.Did you have any issues with the water freezing inside the jar where it sticks above the bowl?I use a kitty litter bucket with horizontal nipples and a small fish tank heater mounted inside. I plug it into a thermocube so the heater only turns on when it's needed. I also have a blue heated dog water dish that perfectly fits a chicken water fount.Blue dish is from TSC, green waterer is from Amazon or Petco, depending on which has the better price. It also comes in a taller size which has the same diameter green part, but holds more water. I love both of them.