What are indications of water in aircraft fuel after draining a sample?

The presence of water in aircraft fuel is a significant concern because it can lead to engine performance issues and potential failure. A solid slug of water or a hazy appearance in the fuel sample clearly indicates contamination, as water does not mix with fuel and will coexist as a separate layer or appear cloudy. Water is denser than aviation fuel and can easily be seen as distinct droplets or a layer at the bottom of a sample container. Hence, any visible indication of water, such as a solid slug or a haziness, serves as a critical warning sign for mechanics to take action, such as draining the contaminated fuel tank and ensuring clean fuel is used.

In contrast, a clear appearance with no particulates suggests that the fuel is clean and free from water or other contaminants. Bubbles forming in the fuel could indicate a different issue, such as vapor formation or contamination with air, but this is not a direct indicator of water. A strong odor and high-density appearance do not specifically relate to water contamination and could arise from other sources unrelated to fuel quality. Thus, the observation of a solid slug of water or a hazy appearance in the fuel sample is the most reliable indication of water presence.