It depends on where you re-fuel.
Any aviation refuelling station gets checked daily by drawing off some fuel, and also the tanks are checked after they are refilled from the truck, which in turn gets checked. Little chance of water there.
Hence the simple fact that pretty much nobody waits for 20 minutes and re-checks fuel, and still aircraft do not fall from the skies.
If you refuel from anything else (jerrycans, barrels etc.), or in rain, have a cup of tea before checking.
All the water-in-fuel related accident reports I remember reading were about either suspected ingress through the filler cap, or contamination in fuel provided from places other than aviation fuel stations or professional bowsers.