PC water cooling pump orings are the seals that keep water inside the pump and out of areas that it’s not supposed to be. PC water pumps move water by drawing it into an intake port and expelling it from an exhaust port, meaning that water is inside the pump itself at all times. The o-ring on the pump serves to keep the water inside the pump and also away from parts on the pump itself that aren’t waterproof. TITAN RIG offers replacement pump o-rings to replace yours in the event of damage during assembly or leakage for any reason. They are economical enough to keep a spare on hand for peace of mind also.