Definition
The presence of water in an aircraft's fuel system, typically caused by condensation inside fuel tanks, leaking fuel caps, or water-laden fuel from a refueling source. Because water is heavier than aviation fuel, it settles at the lowest points of the fuel system, where it can be drawn into the engine and cause partial or complete power loss.
Plain English
Water has gotten into the fuel. Since water sinks below the fuel, it pools at the bottom of the tanks and lines, and if the engine pulls in water instead of fuel, it can lose power or quit altogether.
Context Anchor
Encountered during preflight inspection, especially when checking fuel samples from each fuel drain before the first flight of the day and after refueling.
Why Pilots Care
Even small amounts of water can cause engine stoppage, power loss, or fuel system icing, making it a leading contributor to fuel-related incidents.
Analogy
Similar to water that has entered the gas tank of a car, where the engine coughs and dies because water will not burn.
Grounding Statement
Because water is heavier than aviation gasoline, it can settle at the lowest parts of the fuel system, which is why pilots drain and inspect fuel samples before flight.
Intuition Check
Do not assume water contamination will be obvious by looking into the fuel tank. Water can hide at low points in the system and may only be found by draining a fuel sample.
Example Sentence 1
During preflight, the pilot drained a fuel sample from each sump and held it up to the light to check for water contamination before taxiing.
Example Sentence 2
Any water contamination found during preflight checks must be fully removed before the next flight.