Natures' answer to frozen water tanks or just a myth ?

I also doubt this theory very much. I'd think you'd have to dig down a lot more than a few feet to find ground temps. warm enough to do the job. The water from my well, which is about 160' deep, comes up at about 50 degrees or so. I'm no scientist but I don't think that's warm enough to keep the top of a couple of feet of water from freezing in the dead of winter. But then again, what do I know? The answer to that is, not nearly enough.

Go ahead, start digging. Let us know how it works.

Honestly, the best (and free!) method I've ever used is putting a small ball in the water to float on top - one obviously big enough not to be swallowed by a horse - not as small as a tennis or ping pong ball but not as big as a football (soccer) ball. The ball will float on top of the water and move in breeze or any air movements and this will create a constant movement in the water which will stop it from freezing over completely. I use this in our big water troughs in the fields so the out ponies have a constant water source.

I wouldn't suggest this for automatic water drinkers in stables or small stable buckets - its okay with troughs because there is a bigger area of water so the ball shouldn't get in the way.

The edges might freeze over but the middle shouldn't be covered in ice.

Hope this helps :)

P.S my cheeky pony has learnt how to flick the ball out the trough - luckily he doesn't always manage it!

You have to go down a lot further than that to get warm air rising. As the warm air rises it would be displaced by cold air rushing down the hole and the hole would eventually freeze.

Around here the farmers use solar panel powered heaters. They are portable.

Unless you are sitting over some geothermal source, this won't happen - at least not in Canadian winters where it can get down to -30 C with a wind chill of -45 C.