[masraum]

Originally Posted by john70t

There are retractable pool covers which would keep sunlight and some debris off the water.

An air gap would ensure positive upwards flow of any heat differential: ie pool is warmer than the air.

4 feet below the frost line it's probably about 40-60deg constant which would be a heat sink unless it's insulated.

My guess is that there's not a frost line at SM's yard any more than mine has one. It's probably like looking for a frost line in FL. You're going to be looking until the next ice age.

I have a well for water here and my cold water is ~78º. Some of that warmth is probably from the ground that the water has no run through to get from the well to the house, but that's still pretty warm.