Let the water sit out for days? That works for chlorine in a few hours, but chloramine is a marathon runner. You’d need to wait 24 to 48 hours and aerate it like crazy with a bubbler. Even then, you might only get partial removal.
Does Kdf Remove Chloramine at Anthony Griggs blog
I’ve tried this. I ended up with an abandoned bucket on my balcony that became a mosquito spa. Not recommended. Unless you’re into passive water therapy, move on.