Answer:
Chlorine is preferred over ultra violet radiation because the effect of chlorine lasts longer as compared to that of UV radiation.Though there are pros and cons but the use of chlorine is much much better than UV rays.
The ultraviolet radiation kills the harmful microorganisms present in the water but it does eliminates the extra minerals and salts present in the water that is used for industries and domestic purposes.
Moreover, besides this chlorine has a longer residual effect on the water that keeps the water healthier for a longer time as compared to that of UV rays.