Chlorine and Chloramine are related chemicals that are both regularly used in municipal water treatment. Chlorine is volatile and, if left in an open container, will evaporate out. After 72 hours it will be completely gone. Chloramine on the other hand will not evaporate and must be filtered from the water by other means. A call to your water supplier should reveal which is being used in your area. This was a big concern for me in the days when my
gardening was limited to planted freshwater aquariums in a
city apartment, but personally I wouldn't worry about it in the garden so much. If you have lots of organic matter, a diverse and healthy soil ecology, good fungal networks and such, then they will bounce back quickly from any damage the chlorine might do.