What are the pros and cons when using UV irradiation in water pre-treatment systems?

Pro: The process is relatively easy to explain and the water is not chemically changed during irradiation. An evaluation of the changed water quality during the risk analysis is straightforward.
Con: However, the UV system has the disadvantage of only working at one location in the system. It does not have the depot effect that chemicals have.

[GMP Compliance Adviser, Chapter 5.B]