What is a common disadvantage of using UV light for water treatment?

Using UV light for water treatment indeed has the disadvantage of not providing residual disinfection. This means that while UV light is effective at inactivating pathogens when the water is exposed to it, it does not leave any residual sanitizing agents in the water after treatment. As a result, any contaminants introduced into the water distribution system after the UV treatment can potentially lead to recontamination.

This feature distinguishes UV treatment from other disinfection methods like chlorination, where a residual presence of chlorine remains in the water to provide ongoing protection against microbial recontamination.

Consequently, while UV light serves as an excellent disinfection method for making water safe for consumption, it is crucial to combine it with a method that offers residual disinfection to ensure the water remains safe throughout the distribution system.