R.O. stands for Reverse Osmosis, and you get it either by purchasing the water (where, I dunno..) or by purchasing a unit to do so. They aren't just outrageously expensive, but they ain't cheap either. What it does is basically remove everything from the water, and I mean everything. Then you have to add back what the fish need. The best method of using it is to mix your standard tap water with enough r.o. water to make the measures what you need.
Incidentally, what are the parameters of the water you're trying to fix? My suggestion has always been to keep fish that suit your water conditions, rather than trying to bend the nature of your water to suit the fish you want. Very hard, alkaline water would lend itself very well to a cichlid tank or saltwater...
If you are trying to keep soft, acid water fish like some tetra species, the peat may be your best bet as far as replicating natural conditions goes. The brown color actually looks really nice in the water, but it is kind of "love it or hate it". If the downside in your mind of having tea-colored water outweighs the benefits of a natural solution to your water woes, then there you go....