Minimum should be at least an efficient carbon filter so that the Chlorine and much of the inorganic minerals in water can be reduced. Another way to avoid chlorine is to drink fruit juice. Consider a good diet to detoxify yourself. The Muslims regular and voluntary fasting is good also when it comes to detoxifying the body. Chlorine does not make a person sick at once.
Different persons react differently.
For the average person it can take 10 - 20 years or more if the person does not do anything about it. Even if we get symptoms from Chlorine later in life it might be impossible to know the exact reasons for our symptoms. Our goal must be to minimize all kinds of poisons since it can be too difficult to eliminate poisons totally. But Allah knows best, always. Natural oxygenation treatment are supposed to be widely used in Europe as an alternative to Chlorine treatment.