Sea water is forced at high pressure through the membranes which act as "molecular sieves", only allowing pure fresh water to pass through. Most dissolved solid particles will not penetrate the membranes. This waste, along with the remaining saline solution, will flow on the surface of the membranes and will be rejected.
Not all particles dissolved in sea water can be eliminated. The system is designed to reject 99% of the TDS (Totally Dissolved Solids); approximately 2% of the 35,000 PPM/TDS will pass through the membranes. This guarantees drinking water with a TDS value of 500 (average).
Please note that the drinking water produced by your reverse osmosis system is essentially sterile, however, your fresh water storage should be treated periodically with a slight dose of chlorine (or iodine) to ensure it remains consumable.
Pay attention not to allow pure chlorine (or a too high dose of chlorine) into the desalination system, as this could damage the device.