Welcome to the forum. You'll get lots of hand wringing and teeth gnashing over this one but as for the facts, they are nicely presented in
this document.
I draw your attention to the Canadian rainwater study that found measurable levels of arsenic in water collected from shingles for the first year and then no detectable arsenic after that. The CCA is tightly bound to the wood which makes sense, if the preservative leached out continuously you'd lose the protection. And CCA pine has some impressive guarantees, like 40 year in-ground. It doesn't get the ability to do that by giving up the preservative. I'd suggest that only a small amount of 'contaminated' water would make it into the pool and suffer huge dilution, whilst the purpose of the pool is not a reservoir for potable water, so the amount consumed would be insignificant. In the second year there would be zero contamination. It'll be fine. You better check your local authorities regarding regulations though...
I wouldn't build a roof out of the stuff and collect drinking water though

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Cheers
Michael