Abstract: An oil well rig having a flotatable hull and support legs which are lifted and supported by the floating hull for moving the oil well rig and moved down to engage the sea bottom and jack up or raise the hull above the water at an operating site for drilling or servicing a well or serving an offshore well platform. A water tower has pipes longitudinally mounted by brackets on each side on a beam and is mounted for vertical movement in a well in the hull. An elevator mechanism mounted in the hull is employed to raise and lower the water tower which has guide means fitting a guide portion of the well to provide guided vertical movement of the water tower. When the water tower is lowered, a pump at the bottom of the pipe pumps sea water through the pipe to machinery on the hull to meet the water requirements of the machinery.