Just reading through the CAO 20.2 where it talks about approved methods for testing fuel... it says to put some fuel into the testing container, then add some more from the tanks, and note the demarcation between the two fuels if there is water present.... now it’s been a while since I did any flying.... but I remember just draining the fuel into a tube from the tank... and seeing if there was water that way.... so the CAO say that it was not an approved way to test ?

Commonsense risk management approach -

Now, consider if your fuel tank is contaminated with a significant quantity of water.

You drain a sample (which contains all and only water) … probably looks fine.

Alternatively, you start with a sample of KNOWN fuel .. and THEN drain a sample from the tank. If there is water present, you will see a separation (assuming avgas). [Note, for avtur, things are not quite so clear cut …]

Thanks John... never thought of it from that angle before... after I wrote it... I thought it was a pretty silly thing to ask... but I’m glad it did