- Water Columns are great things for increasing the accuracy of the Water Glass & Water Gauges. The water around the Firebox is boiling rather violently (think of a "rolling boil" in a cooking pot). Pipes fitted directly into the Boiler Shell and Back Head around the firebox have this boiling action passing right across the their ends which can cause surges and suctions in the pipe which in turn will make the water in the Water Gauge "bob" up and down. A Water column acts as a buffer from these surges and such and will give a more accurate reading in the glass. Though they do take up more room in the cab, and are an extra bit of plumbing.