The normal reading of RO pressure for freshwater is:

The normal reading of reverse osmosis (RO) pressure for freshwater is indeed around 500 psi. This pressure is essential for the efficient operation of the RO system since it allows for the effective separation of contaminants from the water being treated. At this pressure, the water molecules are pushed through the semi-permeable membrane, while larger impurities remain on the other side. This high pressure is needed because osmosis naturally occurs at low pressure; to reverse this normal process and achieve purification, sufficient pressure must be applied.

The other options reflect pressures that are either too low or exceed the typical operation range for freshwater applications. Operating below the required pressure may lead to poor filtration, while exceeding it can risk damaging the RO membrane and other system components. Therefore, a pressure reading around 500 psi is optimal for balancing efficiency and safety in a freshwater RO system.