Chlorine breaks down and is gone within 24 hours if you let your water sit out (covered by a cloth to help keep dust and other air contaminants out). However, a caution: Chloramination (instead of chlorination) is becoming more and more common, and it's harder to remove, especially by simple aging. For example, chlorimine has a half life of 26.6 hours even in boiling water (compared to 1.8 hours for chlorine.