Option 1: Use an Electrically Heated Dog Bowl
The easiest way to prevent your dog's water from freezing is to put it in an electrically heated water bowl. Of course, this isn't always an option as you may not have electricity in the area you keep your dog. If you do though, you will need to fill the bowl as much as possible to avoid having to top it off throughout the day. The heat will cause the water to evaporate more rapidly than it normally would, so you will need to keep an eye on your levels to know how often to fill the bowl.
Option 2: Buy a Thick Plastic Dog Bowl
Metal will get cold a lot faster than plastic, which is why it is not ideal for the winter months. With a thick plastic dog bowl, you do not have to worry as much about the bowl itself causing the water to freeze. The air above the water will still cause the temperature of the water to drop, but the container will do its best to keep the water from freezing.
Option 3: Surround the Water Bowl with Styrofoam
Styrofoam is a great material to use for cheap insulation. If you have a small dog or a cat that stays outside, you could keep your water bowl in a Styrofoam cooler and cut an access hole in the side. Aside from that, you could buy Styrofoam rings from a craft store to put around the outside of the bowl. This will insulate the contents and keep them as warm as possible.
Option 4: Get a Deep Water Dish
Deep water dishes are much more likely to keep the water warm than shallow water dishes. Of course, you have to keep your dog's body structure in mind. If your dog has a short neck, a deep water bowl may be too much for him to get into. Get the deepest dish you can while still thinking about how your dog will be able to use the bowl itself later on.
Option 5: Keep the Bowl Inside
Ideally, your dog and his water dish should be kept inside in the winter. This doesn't necessarily mean they have to come inside your house. You may put a doggy door on your shed to let your dog come in and out freely, or you may invest in an oversized dog house for the winter. That's where you can put the food and water, along with anything else your dog may need to stay warm.
No matter what you do, keep an eye on your dog's water levels throughout the winter to ensure he stays healthy and hydrated.