System and method for improving immersion scanner overlay performance are described. One embodiment is a method of improving overlay performance of an photolithography immersion scanner including a wafer table having lens cooling water (“LCW”) disposed in a water channel therein, the wafer table having an input for receiving the LCW into the water channel and an output for expelling the LCW from the water channel. The method includes providing a water tank that connects to at least one of the wafer table input and the wafer table output; monitoring a pressure of water in the water tank; and maintaining the pressure of the water in the water tank at a predetermined level.