When the weather turns cold in the winter months, there's a real possibility that the water in your outdoor pet's bowl could freeze and stay frozen throughout the day. Although some animals can eat the ice, many won't, so it's important to be prepared and vigilant.
Fortunately, there are plenty of ways to counteract cold temperatures depending on your pet's needs, your budget, and the amount of time you have to pull something together.
Although it's not free and you'll have to wait for it to ship, the simplest solution is buying a heated bowl. They come in solar-powered and electric varieties, and can keep a bowl warm throughout the day. On the whole, they're popular and many pet owners love them, but they come with a few drawbacks: first, you're limited to a certain type of bowl, so if your pet is better served by a bowl with a different size or material, you're out of luck. Also, if you have a pet with a chewing habit, the cord to the bowl could be a tempting and dangerous object to have within their reach. Finally, you'll need to plan in a small increase in your electric bill if you get an electric bowl, as it stays on as long as it's plugged in.
If you have dogs or cats sleeping outdoors in a pet house, consider placing an electric heated pet bed under, next to, or inside it to help keep your pets warm and prevent their water bowl from freezing. It's advisable to not set the bowl on top of the mat to avoid potential spilling accidents.
Since it's the 21st century you probably already have a weather app on your phone, but there are a few more advanced weather apps available from Weather.com that will alert you of extreme weather conditions on the horizon, so you can be prepared to keep your pet's water from freezing.
If you know your pets are likely to eat their dry food soon after you set it out, you might consider mixing in a little water. Not only will the water be less likely to freeze when it's absorbed in the food, it makes sure your pets stay hydrated in the event of a freeze. Although it's not a good long-term strategy, adding water to your pet's food makes for a good quick fix while you're working on implementing another solution (e.g. waiting for a heated bowl to ship).
This, like adding water to their dry food, is more of a quick, temporary fix. Adding a little bit of oil, sugar or salt to your pet's water will harmlessly lower its natural freezing point. Unless you're already supplementing your pets' diets with these ingredients, it's probably not a good idea to do this often, but if you're in a tight spot it might do the trick for a night or two.
Water is good at holding onto its own heat as long as it's insulated from outside sources of cold. If you live in a climate that rarely dips below freezing, keeping your pet's water in a Styrofoam container or cooler will help it stay above its freezing point. For larger animals, you could try filling up an old car tire with rocks or gravel and setting the bowl in the opening to make sure it stays stationary and insulated from the cold.