Old pictures, but that clay pot is what I and many others use here.
The opening is small enough to stop the dogs, sheep etc from drinking from it. The clay helps to keep the water cooler in the summer months. They don't freeze as quickly in the winter as plastic containers. The drinking cup needs a scrub out from time to time, or you can put a small amount of oxine or even vinegar in the water to combat the slime build up.
I have these dotted about the place.
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