It's my opinion that a carbon-block prefilter and an RO membrane are all you need for your average tap water. If you're using well water you'll need some sort of sediment filter in front of that.
The membrane produces nearly perfect water all by itself. What you need the carbon-block prefilter for is to remove chlorine, which will eat away at an RO membrane and create openings for solids to fit through.
I've been using the same $75 unit with a prefilter and a postfilter (which I consider useless and never replace) for seven years or so. I've been very lazy about replacing the prefilter -- you're supposed to do it every 6 months, and I do it maybe once every 18.
Today I still get these results on the TDS meter:
tap water: ~125 ppm
Brita filtered water: ~75 ppm
RO filter: under 15 ppm
I can't imagine anyone but a scientist or an engineer needing better than 15 ppm.
So, yeah, don't waste money on anything fancy.
Carbon, would you mind letting us know what brand you have and where you got?
If your city water runs a TDS above 150, it is helpful to have a sediment filter to keep your carbon block from getting clogged up with sediment.
Sediment cartridge, carbon block, RO membrane.
I have used a couple units from airwaterice and every one has worked well and lasted. I don't have any affiliation with them, and some of the dendroboard sponsors also sell acceptable RO units.
Stay away from anything with the Coralife name on it.
I do not have a TDS meter so not to sure how bad my city water is.
I was looking at this site:
Build Your Own RO System - English
It's a build your own part of their website.
Stage 1 offers:5 micron and 1 micron sediment
Stage 2 offers: same as above plus 5 micron and 1 micron carbon block
Stage 3 offers: same as above(carbon) and Deionization Resin(color changing)<~~~~ whatever that means and a Chlorplus carbon block
Stage 4 (membrane) offers: 75 GPD which is WAY MORE than I need but the lowest they offer
Stage 5 offers: single or dual DI
I understand all those stages are overkill but do I need the DI for anything? and I think the Stage 1(5 micron sediment) would become clogged very quickly, wish they offered like a 15 or 20. And I assume that I would just need the 5 micron carbon block.
I really don't see the need for anything that is a 1 micron, please correct me if I'm wrong.