The amount of chlorine used by your water provider depends on the source of your water. If your source is groundwater well field, you are lucky because the amount of CL2 used is minimum and by the time the water reaches your tap, most if not all Cl2 is gone. If your source of water is from river, you are unlucky because river water has high bacterial count and more Cl2 is used. Reservoir water is somewhere in between in term of CL2 treatment. In summer months when there is frequent storm runoff into the river or reservoir, maximum Cl2 treatment is used and you have to be vigilant to add enough dechlorinizer in water change. Also, right after water pipe repair work, water company will super chlorinate the exposed section of the pipe to kill germs so you should never do water change right after water outage.
