On a boiler, the water column:

The water column plays a crucial role in providing an accurate and stable reading of the water level in the boiler gauge glass, which is essential for safe and efficient boiler operation. By reducing turbulence in the gauge glass, it enables clearer visibility of the water level, allowing operators to monitor it accurately without erratic fluctuations that might mislead them about the true water level. This stability is vital, as improper water levels can risk overheating or damaging the boiler, leading to potential safety hazards.

In terms of the other functions mentioned, measuring inches of H2O typically relates to how water levels are quantified, but that is not the principal function of the water column itself. While the hydrostatic test is important for checking the integrity of the boiler, the water column is not directly involved in that process. Feeding water into the boiler is generally a function of the feedwater system, rather than the water column's role, which is focused on level indication rather than water supply. Thus, the primary role of the water column is establishing a clear gauge reading by minimizing movement caused by turbulence.