You need to know what is in your water and what it needs to make it better for brewing.
A RO unit if it is well looked after (many aren't) will give you a pretty blank slate, you would be wanting to add some salts especially Calcium as 50-100ppm of Ca is regarded as a minimum.
My local water is good (they mostly use Chlorine rather than Chloramine), if anything a bit light on for most minerals, for some styles I use a two stage filter (particulate then carbon) followed by UV steriliser if it's necessary. For yeast I use
Pureau water from woolies, its about as 'pure' as you can get.
If you just want to get rid of Chlorine/Chloramine I would use Potassium/Sodium Metabisulphite (Campden tablets), would only be bothered boiling if there was a lot of Bicarbonate in my water... do what is necessary to improve the water I have.
There are several threads on local water analysis one called "big thread on water around Australia" or something like that, look at your local water analysis there if you can, or on your local water authority website, work out what you are trying to achieve and go from there.
Mark