A subsea system for injecting seawater into a subterranean formation comprising: a sub-micron filter module configured to accept incoming seawater from an inlet and use cross flow filtration to separate the incoming seawater into rejected seawater and sub-micron filtered seawater , wherein the sub-micron filter module comprises a particle filter , a micro-filter downstream of the particle filter and a nano filter downstream of the micro-filter ; an injection pump configured to accept the sub-micro filtered seawater and increase its pressure for injection into the subterranean formation via a wellbore penetrating therethrough; and an auxiliary pump positioned downstream of the nano filter , the auxiliary pump having an inlet connected to accept the rejected seawater ; a choke valve disposed between an outlet of the auxiliary pump and the sea, the choke valve configured to be selectively opened so as to provide a first flow path for the rejected seawater to the sea; a first ejector coupled to an inlet to the particle filter by a first valve ; a second ejector coupled to an inlet of the micro filter by a second valve ; a third valve disposed between the outlet of the auxiliary pump and the first ejector , the first and third valves being configured to be selectively opened while the choke valve is closed to provide a second flow path for the rejected seawater through the first ejector to backflush the particle filter ; and a fourth valve disposed between the outlet of the auxiliary pump and the second ejector , the second and fourth valves being configured to be selectively opened while the choke valve is closed to provide a third flow path for the rejected seawater through the second ejector to backflush the micro filter . a sub-micron filter module configured to accept incoming seawater from an inlet and use cross flow filtration to separate the incoming seawater into rejected seawater and sub-micron filtered seawater , wherein the sub-micron filter module comprises a particle filter , a micro-filter downstream of the particle filter and a nano filter downstream of the micro-filter ; an injection pump configured to accept the sub-micro filtered seawater and increase its pressure for injection into the subterranean formation via a wellbore penetrating therethrough; and an auxiliary pump positioned downstream of the nano filter , the auxiliary pump having an inlet connected to accept the rejected seawater ; a choke valve disposed between an outlet of the auxiliary pump and the sea, the choke valve configured to be selectively opened so as to provide a first flow path for the rejected seawater to the sea; a first ejector coupled to an inlet to the particle filter by a first valve ; a second ejector coupled to an inlet of the micro filter by a second valve ; a third valve disposed between the outlet of the auxiliary pump and the first ejector , the first and third valves being configured to be selectively opened while the choke valve is closed to provide a second flow path for the rejected seawater through the first ejector to backflush the particle filter ; and a fourth valve disposed between the outlet of the auxiliary pump and the second ejector , the second and fourth valves being configured to be selectively opened while the choke valve is closed to provide a third flow path for the rejected seawater through the second ejector to backflush the micro filter . <EOS>