In practice only the topsoil will be polluted and degraded? Now that's a relief. No, seriously. Beside the yet mostly unknown health risks and unknown chemical reactions of chlorinated water in the landscape there is one aspect that should make you think: When you water your garden with chlorinated water all the negative loaded minerals will be gradually washed out of the soil, e.g. phosphate, sulfur, nitrate. Because chlorid is blocking all the positive loaded anodes with an anion. It is highly reactive. Watering with chlorinated water has a cumulative effect on the soil, too. In the end you have to use mineral oil fertilizer to replace your missing nutrients.
In Europe it is forbidden to water plants with chlorinated water that serve humans directly or indirectly (e.g. cattle, chickens) as a food source. It is also strictly forbidden to empty your swimmming-pool's content in the landscape.
In Germany there is no intentional chlorination, the tap water is high standard drinking water. We use ozone and ultraviolet radiation to desinfect the drinking water.