Recommended Filter Array
The idea behind an array of filters is to provide for optimum pressure and a long filter life. The pre-filter micron rating required to optimize the life of a reverse osmosis membrane is five micron. No manufacturer asks for more protection than that and nothing is gained by smaller micron filters. In fact, you only hurt the overall performance of the system by using smaller micron filters. How do you hurt it? By causing excessive pressure drop.
Never install a one half (0.5) micron filter as a pre-filter. A filter array is designed so that each filter does the work required of it and protects the next filter in line. It would make no sense to dump big particles of dirt on a fine filter. You would clog it up immediately causing a great deal of pressure loss.
What I now recommend is: Get a ten micron sediment filter for your first stage, no smaller! Then obtain a good quality five micron carbon block, acid washed filter for the second stage. The ten micron filter has removed all of the dirt and sediment over ten microns from the water which protects the five micron filter. Now, all the five micron filter has to remove is sediment between 5 and 10 micron. In the third stage get a quality one micron carbon filter or a sediment filter if you have well water. You have now accomplished filtration down to one micron, five times the manufactures requirements. You have not lost a great deal of pressure and the filter can now provide you full service. So to recap; the ten protects the five, the five protects the one, and the one micron exceeds the requirement to protect the membrane by a factor of five, so your membrane sees only one micron sediment... one fifth the requirement.
Protected by a 10-to-1 micron array, the membrane is free to go about the task of removing bacteria, virus, salt, ions and dissolved metals (TDS). The filters alone have no impact on the TDS and should never be relied on to remove bacteria. Ions and bacteria are best left to the membrane. After the work done by the pre-filters and membrane, your water is very pure. The final stage is DI -- A typical mixed bed DI cartridge is capable of reducing the TDS to zero (0).
