The “water in fuel” business is debatable.
Avgas will hold up to 0.1% in solution. Anything above that will remain separated.
One view is that it takes some hours for the liquid water to settle on the bottom of the tank, so there is no point in checking if the plane has just been moved around. I think that must be right.
In my PPL training days, in a totally shagged PA38 with nonexistent fuel cap seals (the operator was a CAA AOC holder so that was par for the course 
) I drained several beakers (perhaps half a litre) of clear water before any avgas started to come out, and it was only a sharp-eyed FI who spotted the colour difference, so if you fill up a plane with water instead of avgas, a lot of people would never notice.
I watch and smell at the content of the drain bottle, just to be sure it’s avgas 
I am not as ‘water-paranoid’ as some. I’ve never detected any significant water at all in any fuel sample I’ve collected, and to my mind the colour/smell/feel and rapid evaporation of avgas means you’d need to be fairly unobservant to mistake water for it. The perished/absent fuel cap seals problem is inexcusable and trivial to fix.
Beyond the amount it’ll hold in solution I wouldn’t think it’d take much time at all for the water to settle at the bottom. If your tanks are odd shapes you might not get it all where you expect, but in normal circumanstances I don’t see why any immiscible and heavier liquid in with the avgas should take any significant time to settle. Fill a small see-through container with part water and part avgas, shake it about a bit and see how quickly it separates and settles.
These days I’m reluctant to disturb fuel drain valves unless I perceive a particular contamination risk because they can be reluctant to close properly.
An engine will lunch a fair amount amount of water without too much of a problem as long as it isn’t asked to run on pure water. If we assume some nominal small amount of water sitting in each tank, prob99 the engine will lunch it during startup, taxiing out and power checks. Another reason not to rush on the ground and allow normal operating temperature to be reached.
At Cannes airport the safety manager was not specific about what form of contamination was in discussion (they didn‘t find any). Therefore, I checked not only for some water residue (there was a small amount to be found, but nothing different to other airports when the airplane sat outside in humid and warm air for several days). The check for a residue of jet fuel was a first to me in my 30 years of flying.
The Twin Com can be intolerant of rain, and being left outside. There have been instances before of both engines stopping in a PA30.
https://assets.publishing.service.gov.uk/media/5422ff1240f0b61342000903/10-1975_G-ATYR.pdf
G-ATYR_pdf local copy
There have been a lot of instances for Twins to stop both engines within minutes, including most of all fuel starvation. As long as no further report is available from the TwinCo it is difficult to speculate.
I don’t know why the TwinCo should be any intolerant to being left outside. The filler caps and the additional lid above it are really tight.
Regarding the report of the G-ATYR to me this sounds like Mafia involved a passenger lost, no traces found, believed to be dead, that story was written more often than once
WilliamF wrote:
The Twin Com can be intolerant of rain, and being left outside. There have been instances before of both engines stopping in a PA30.https://assets.publishing.service.gov.uk/media/5422ff1240f0b61342000903/10-1975_G-ATYR.pdf
G-ATYR_pdf local copy
That report suggests that they considered fuel contamination pretty unlikely?
UdoR wrote:
I don’t know why the TwinCo should be any intolerant to being left outside. The filler caps and the additional lid above it are really tight.
Agree Udo, they are exactly the same as on the singles and are not vented and enclosed with the similar door as on the single. I would consider the TwinCo less prone to water contamination versus other planes. Have never found any water in our tanks. (remember the tanks are also the ones that have a ’’plastic’’ bag and the fuel does not touch the wings directly. This helps with condensation as well.
Graham wrote:
I am not as ‘water-paranoid’ as some. I’ve never detected any significant water at all in any fuel sample I’ve collected, and to my mind the colour/smell/feel and rapid evaporation of avgas means you’d need to be fairly unobservant to mistake water for it. The perished/absent fuel cap seals problem is inexcusable and trivial to fix.
You’ve been lucky.
LFHNflightstudent wrote:
I would consider the TwinCo less prone to water contamination versus other planes.
The twin com has a door with seals that benefit from a replacement, the original tank bung style caps are usually well worn at this stage and replacements are better. I’ve seen the drains blocked and the telltale signs are corrosion in there, on the auxes it sometimes you see corrosion around the sender. The previous owner of the twin com I had didn’t seem to give a flying -d-uck about the above. The Comanche forums are full of water stories, I’ve read all the ICS notes on the fuel system and water is a recurring theme. When I ran the PA30 it was always with 1% IPA mix in the fuel to aid the pick up of water.
When you consider something like the late model fuel cap on a Cessna, I know which one I’d prefer to rely on.
