I just carry a pitcher of warm water out at least twice a day and pour in the black rubber tub. If the ice is on the thick side, I have one of my ds break it with a stick first, then add the warm water.
If an animal has a chance to drink at least twice a day, they'll be fine. I know humans are brainwashed lately that if all organisms don't have fresh, pure, crystal spring water every 15 minutes we'll dehydrate up and die, but that's just not true. Animals have been watered twice a day for centuries and done well, been productive.