What can be a visual indicator of water in fuel?

A visual indicator of water in fuel is the separation of layers in the fuel. This occurs because water is denser than fuel and does not mix with it, leading to a distinct separation. When you look at a container of fuel that contains both fuel and water, you can often see a clear demarcation line between the two substances, with water settling at the bottom and fuel above it. This phenomenon is crucial because water in fuel can cause engine performance issues, including corrosion and difficulties in combustion, making it essential for aircraft operators to check for such indicators during pre-flight inspections or fuel management practices.

The other choices, while they may relate to broader fuel system issues or engine performance, do not serve as direct visual indicators of water contamination. High fuel pressure readings could indicate a variety of issues in the fuel system, low RPM at idle is typically a symptom of engine performance problems, and excessive oil consumption could point toward engine wear or other mechanical problems. None of these options provide a clear visual indication like the separation of layers does.