You should do the treatment on a POE/whole house basis.
Depending on what and how much of it is in your water, like iron, hardness, H2S etc. etc. you may not be able to use a UV light as POU or POE (point of use or entry), or you will need pretreatment like a softener etc..
Otherwise UV is a good way to go unless your pretreatment requires chlorine or other disinfectant.
So get a water test for those things, expect H2S and post the results including the nitrate and nitrite levels.
BTW, UVs can have monitors to tell you if it is working correctly on not but you need to replace the lamp and clean the quartz sleeve every year regardless.