This needs to be considered ...

This needs to be considered along with the microbial risks that are in the water. We have a lot of UV units, most of which have only residual disinfectant. However, we do have some sites where we are aware that there is a pathway for faecal contamination and therefore viruses. UV is not wholly effected against all viruses so we have chlorine contact to deal with the potential presence of these.

In short - it's not a one size fits all approach and is all about the risk management of the raw water

Hope this helps