Hi Charles
In practice, the two steps are used in combination. Needless to say the more hurdles in place the better. For packaged waters not claiming Spring or Mineral water status you would typically go for combined
CCP's. Others can be used including RO, Ozone etc.
The UV system depending on its capacity will achieve a certain log reduction in the total count and should be sufficient to deal with certain pathogens including E. Coli. (Of course all this needs to be validated - flow rates, incoming loads, lamp intensity and so on...) Pathogens such as cryptosporidium may not be killed by UV and this is one of the reasons why .2 micron filtration may be used. It's worth noting that under various standards and legislation, Mineral and Spring Waters are not allowed to be treated (a couple of exceptions are allowed) and therefore UV would prevent use of this designation. Source water would need to be to standard...
George