Boiling it is not an option...???
We have a fire pit and large pot for such things but I see your point.
Looks like the pool becomes a bathtub of sorts.
Boiling is necessary for distillation, but boiling itself will only kill pathogenic microorganisms and remove a significant portion of any volatile organic compounds that are dissolved in the water. To make the pool water suitable for consumption, you need to actually distill it: boil it, capture the steam, condense the steam back to clean water. In addition to your boiler, you'll also need something to catch the vapor and condense it, much like the copper coils you see on a 'still for making moonshine, and then collect the condensate (which should be water as pure as you can get it) in a clean container. It's a very fuel-intensive process, which is why most industrial deionized and/or purified water is processed via reverse osmosis rather than distillation.