The performance & efficiency of a Reverse Osmosis (RO) system depends upon the membrane type, flow control, feed water quality (contaminants & quantity, pH, turbidity, total dissolved solids; TDS), pressure & temperature.
RO systems require a reasonably high pressure in order to function properly. Most domestic RO systems require 400kPa (60 psi) to operate efficiently and maintain performance. A minimum operating pressure of 350kPa is recommended however the units will operate down to 240kPa although this will affect the quality of water produced. If the water pressure is too low the RO will not be able to overcome osmotic pressure (the bonding between water molecules and the dissolved impurities). The higher the contaminant or TDS level, the higher the osmotic pressure. If the water pressure is too low the treated water production will be less efficient and the contaminant rejection rates much lower resulting in poor quality treated water.
A boost pump can be added to an RO system to increase the pressure and improve the quality and quantity of water produced.
Bench top RO systems are able to operate at lower pressures than under bench systems due to the fact that they do not have to work against back pressure created in the storage tank as it fills with water and compresses the air in the tank.