The only water it gets nowadays is from rain, or snow. It has been a very water worthy pool bed - it did not leak, at all! In the depths of one winter it got full to the brim before I realized I needed to sump pump this pool during the rainy season. And so I've been ever since.
But, finally, I've decided to make a big planter out of it. And today, the first step (beyond me making such decision) was to have the bottom jack-hammered and broken up. Next is putting gravel in the bottom; then garden soil; then the drought resistant, water-wise planting.