I have posted on the topic more than once about chlorine and chloramine.
Your are 100% correct that you can gas off chlorine the best way to achieve this is to put an air stone in a bucket of water in a dark place and let it bubble for 24 hours the bubbling affect will release the chlorine faster.
Now chloramine doesn’t gas off like chlorine. You need to call your water company and request what’s product in your water. They have to provide you with this information at least in Canada they do. They will even provide lab reports on the make up of the water.
Since my water supply consist of chlorine I haven’t done a lot of research on chloramine but I did read a article before that says you can put the drops in for fishtanks and it will remove it but you’d have to do your own research to confirm this
Before my Ro system I always Bubbled my water