Check your dog's shelter and water through the day and at night to ensure that his bedding is dry and that his water is not freezing.
Don't place water in your dog's shelter; it may spill in the course of the day or night and freeze his bedding, turning his warm sanctuary into a walk-in cooler.
A bowl that holds a large amount water will take longer to freeze than a bowl that holds less.
Using hot water won't necessarily slow the freezing process. Hot water freezes faster than cool or tepid water due to a phenomenon called the Mpemba effect.
Your dog needs food, water, shelter and exercise no matter what the weather is. If winter temperatures dip below freezing where you live, you must ensure your dog's accommodations are winter-ready. Short-hair dogs need to come inside when temperatures are in the 20s Fahrenheit; long-hair dogs can stay out until it's a little colder. But when they're outside and the temperature's freezing, you must ensure their water does not freeze. Options abound.
Consider a commercially available electric heated water dish to keep your dog's water from freezing if you can safely run power to your dog's shelter. Select a large dish with a chew-resistant cord if you can. Place the dish near, but not in, his shelter. If it's in his shelter and it spills, your dog will be worse off. Water in a heated dish can evaporate quickly, so plan on refilling the bowl with a gallon of water every 24 hours.
Ask your area extension agent if your region gets enough sunlight to make a solar-power heated water dish a value purchase. A solar-charged element will keep a water dish from icing up overnight, but it could lose its charge if too many days pass without sun. A battery-operated immersion heater is another option for keeping your dog's water liquid in freezing temperatures without resorting to plugging into the grid. It's handy to use in combination with a solar heater during stretches when the sun goes unseen.
Place a microwavable heat disc underneath the water bowl. Pet supply retailers carry these round warming devices in various sizes and colors. They typically serve as bedding warmers; in below-freezing temperatures, a properly heated one will keep a water dish warm for up to three hours.
Keep a spare bowl on hand so you can cycle through water bowls throughout the day. Check the bowl regularly, switching the bowl as necessary -- the size of the bowl and the temperature will dictate if you need to change his water hourly or every few hours.
Take a page from horse owners and use sunshine, rocks and an old tire to make a solar warming station: Position a tire in a sunny spot of your yard, close to your dog's shelter and out of the wind. Gather a variety of rocks of different sizes and fill the tire with the rocks. Place a thick plastic bowl, bucket or Styrofoam cooler in the center of the tire, surrounding it with additional rocks so they are almost level with the rim of the bowl. Fill the container with water. Use a plastic bag liner if you use Styrofoam. The tire and rocks should radiate enough heat to keep the water from freezing for hours after the ambient temperature has fallen below freezing, but you must check it regularly to ensure it doesn't freeze.