Although water is scarce in winter, birds still require fresh water for drinking and preening.
Birds may be hungry in winter with so few food resources, but an even bigger threat can be dehydration. With many water sources frozen over, birds have hard time staving off dehydration. Birds can eat snow, but they do need to use energy to bring snow to body temperature. There may be access to unfrozen sections of ponds or streams, however, it may take energy to get there.
Not only do birds need water to drink, but they require water for preening. Preening keeps feathers aligned, which means birds are able to properly insulate their bodies, helping to keep much needed heat. When birds can’t preen, and their feathers are out of alignment, they lose body heat much faster than they would otherwise.
But you can provide birds with fresh water sources by either providing a heated birdbath or adding a heating element to a birdbath you already have. You can add hot water to melt ice in your birdbath, although it will freeze again. You should NEVER add anything but water to your birdbath. DO NOT add anti-freeze, salt, or other chemicals, such as glycerine.
Birds are survivors, but they rely heavily on us for not just food but also water and areas to nest. Helping birds with access to fresh, clean moving water just increases their chances of survival.