Many areas of taiwan are on wells and ground (water/soil) contamination is a big problem here. My rule is to boil first (i do 20L batches to make it easier), let cool then filter. Boiling kills stuff. Filter takes out things above a given particle size( be it biological or heavy metal or…)
Water here isnt great in my opinion. So i would filter for sure. But do both.
Note that a lot if water stations whee you fill your 10L tub for 10nt (20 or 30 in cities) are often corrupted. Not all are RO, most probably are UV blasted but their systems, when you look at them, clearly are not thought out well and effective. So definately take matters into your own hands. I was sick for a fairly long time. Afterwards realized it was they were not actually RO, filters missing and just bypassing, UV was there but small bulbs and wont penetrate a 3 meter deep tank (literally just wired on the top haha) amd dead rats were common. Interstingly all the aboriginal guys knew about this but we never heard in the hakka town about it until a few years later. Cities arent a whole lot more diligent…so unless you get government piped water, worry.
If youre in very developed areas and or clean areas like certain spots in Taipei, Taitung, high mountains maybe someo trust is ok. In places like Tainan though, sorry.