The chlorine in water will evaporate into the air if left in an open container; Pour yourself a glass of water, and let it stand for 30-60 minutes. It should then taste a LOT less Chlorine-y. Even in a sealed container you shouldn't be able to taste it after about 3 days. This is why water from a mains pipe tastes of chlorine, but the same water pumped into a water tank (for heating etc), doesn't.
