Sediment and carbon filters have nothing to do with final TDS, they protect the RO membrane so it lasts longer and works better. This is why Spectrapure systems last so much longer, give you lower TDS and cost less to own. I'm over 5 years on my present membrane using Spectrapure replacements and even stretching their schedule a lot. I am sure you have heard of Randy Holmes Farley; He reported 10 years on a Spectrapure membrane still at high rejection rates before replacing it. There really is a difference and its the complete package, sediment filter to DI resin and every thing in between. You get what you pay for and I would never go back to anything else I have ever owned and tested in the past. You can use a god membrane or good DI resin but if you do not protect the well with good sediment and carbon filters and a good, properly sized and trimmed capillary tube flow restrictor and monitor what is going on you are wasting money. Yet another time, there really is a difference.