I have a 7 stage RO system which i bought off ebay for €130 and i'd happily put it up against any bottled water you care to name for both taste and purity.
the last of the 7 stages is a re-mineralisation filter which puts back all the good stuff that gives you the desired flavour in the water.
the water is also as soft as it gets and as a result of using it, the inside of my kettle looks quite literally like it's brand new, despite having previously being covered in limescale from the crappy water we have in Dublin 15.
I used to live in Navan which is traditionally a hard water area, but when we moved to Clonsilla before xmas, it was at a whole new level and the tap water was barely drinkable and as well as stinking of chlorine, it was off colour and contained some sediment.
we had fingal co. co. out to do water tests, but they concluded that the water was within the EU guidelines and that was as far as they were willing to go, so I had to take matters into my own hands as the whole family were starting to get skin problems from showering and washing in the water and with a 9 month old baby, i had to do something about it and an RO filter system seemed to be the answer.
i managed to catch an ebay auction ending when it was really quiet and got the whole €260 thing for €130. it took less than a week to arrive and about an hour to install, even with my own very limited DIY experience.
I've since added a hydraulic pump (powered by the water pressure) to increase the output and i'm planning on adding a 2nd RO membrane and a bigger reservoir (16L, up from the 8L it was supplied with) to allow me to supply the whole house, rather than just our drinking, cooking and hand washing water, but I'm very happy with it so far and would highly recommend it to anyone who has problems with their water supply.
personally, it's worth it just to have clear ice cubes instead of cloudy ones.