Hi all,
I just wanted to post a little update on my waterers. I have the plastic ones (with the spring) and have been using them for 2 years now. However, 2-liter bottles really don't work with them - they're too fat. But tall, skinny bottles work well - 1 to 1.5 liter bottles. Usually the high end brands of bottled water (esp. that you find in health food stores) have these. Each waterer rests on an 18" length of PVC pipe to keep them level and the bottles are held in place with a bungee cord.
If you have freezing weather in the winter, you need to check them every so often to make sure the water in the resevoir and at the bottle opening hasn't frozen. I usually bring a pitcher of hot water with me to melt the ice and add to the bottles.
I really need to replace them, and I'm going to try the aluminum ones that Lollypop suggested from Cutler Supply.