From the National Wildlife Federation  https://blog.nwf.org/2014/12/dont-forget-water-for-birds-in-winter/

Here are some tips for easily—and safely—providing water for wildlife during the cold months:

1. Before the cold sets in, replace delicate solar or fountain birdbaths with sturdier, winter-ready water features. Because ice can cause cracks and leaks, concrete baths should be stored or covered in winter.
2. Place baths in a sunny area to make them more visible to birds and to help keep the water liquid.
3. While birds are unlikely to submerge themselves in very cold weather, you can help them stay dry and drink more easily by adding several stones to the bath or placing a few sticks on top that the animals can use as perches.
4. Even during winter, birdbaths (as well as feeders) should be cleaned regularly.
5. To keep water from freezing, consider adding an immersion-style water heater. More recent models will turn off if the water in the bath dries up.
6. If using a heater, add a ground-fault interrupted circuit (available at hardware stores) to prevent electric shorts. Check that cords and outlets are sheltered from snow or ice buildup.
7. As a homemade alternative to a heater, place a light bulb in a flower pot and put a small water basin on top of the pot.
8. A simpler option—particularly if you have no outdoor electric outlet—is to buy several heavy-duty plant saucers that will not be cracked by ice and replace frozen baths with fresh ones each morning.
9. Avoid adding glycerin to a birdbath as antifreeze; if birds ingest too much, it can dangerously elevate their blood-sugar levels. Glycerin solutions also may mat birds feathers, decreasing insulation at a time when the animals need it most.

Posted by: Carlotta Lucas,

Photo by: Jocelyn Anderson, CC BY 3.0 https://creativecommons.org/licenses/by/3.0, via Wikimedia Commons