Yes, galvanized waterers rust out and have to be replaced every two or three years, but you can place them on a heater and it works great. Love to see that steam rising from the waterer on a cold morning.
I have several plastic ones that I seldom use any more because they get algae inside and are hard to clean. Also it's hard to screw the top on tight enough to keep them from leaking.
I had been using an old dog bowl that held about two gallons out in their yard, but with 30 chickens now, it was going dry too quickly. I bought an automatic waterer from McMurray. It's a long trough with a hose connection at one end and a float valve to shut it off when it is full. It has anti-roost wires on top. I like it, BUT.....the first one leaked at the connection and also the trough itself leaked. I called them and they sent another one.
The connection still leaks a little, but not enough to stop using it. What I do is turn the water off at night (the trough is out in their yard) to keep from wasting so much. There is a constant but slight trickle of water at the hose connection. This winter I will take it apart and see whether I can really fix it. It was around $100 with shipping. Trifle overpriced in view of the poor performance. Just IMHO.