I'm setting up my studio in my home and due to safty concerns with the different gases, I'm thinking about purchasing a water torch. But, how big of a piece can you anneal (if at all) with a water torch?
If you have natural gas to your home you might consider a torch that can be used with that fuel. I do not recommend propane as a fuel if you will be storing the tanks inside since the tanks discharge periodically and propane can collect in low pockets on the floor. If you store tanks outside then most any fuel used is safe as long as you use standard safety procedures when using the torch.
Water torches are hydrogen fuel torches and will work fine. I do not know if the flames generated are large enough to be used in annealing. I suggest you contact the manufacturers of these torches and ask them. The facility where I taught purchased a water torch and abandoned it after a few times use. As I recall it only had fine tips and was intended for fine jewelry scale items.