The primary goal of a Spectra RO (Reverse Osmosis) system is to purify seawater (36,000 ppm) into drinking water that has no taste of salt (<750 ppm). The biggest hurdle is removing small salt ions (NaCl). Reverse osmosis membranes have pores that are large enough to allow water molecules (H20) to pass through but small enough that salt ions cannot. Our membranes are designed to reject 99.4% of salt and similar sized ions. If your system is working (able to take out more than 98% of the salt in the water) than it will also take out bacteria, viruses, or heavy metals which are between hundreds and millions of times larger than a salt ion.
The only reason that there are prefilter cartridges (5-micron) on our systems is to keep our pumps and membranes clean. Additional prefilter cartridges can be added to the system to help extend the length of time between filter changes, however this does not impact the quality of the product water.