we bought two galvanized livestock water tanks from a local feed store. One is five feet in diameter and the other is six feet in diameter. We then nested them, leaving a gap on both sides and on the bottom. We filled this gap with that canned spray foam to create an insulated barrier (the last three inches around the top we filled with concrete for a better aesthetic). For plumbing we simply provided two openings for filling, draining and circulating.
Dream Water Gardens...Down on the Farm Galvanized stock tanks, which typically hold water for livestock, are perfect for an easy-to-build water feature. Ornamental windmills spin in the breeze, complementing the farm feel of the tanks.