I keep jugs and rotate them like other people have mentioned (mostly to allow it to acclimate to room temp) and I know chlorine will evaporate over time but, in most cases it shouldn't harm your animal. Years ago people would fill fish tanks and through the process of balancing the water and adjusting temp, enough time (24H or so) would pass that folks didn't feel the need to condition the water. I was one of those. I don't believe this is considered a best practice now.
This is a small thing, water conditioner, to be debating.
If there were a problem, then someone here would surely voice it.
However, I would still encourage you to keep reading and then learn through your own husbandry.
If you are concerned and the treatment is not harmful to your animal then better to err on the side of caution.
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