I'm more than surprised that a Shell refueller advised that the syringe/capsulre test is an overkill for turbine engines.
A positive test for water in suspension does not necessarily mean that engine problems will occur, but it warns that the concentration is sufficiently high to enable water to condense out of suspension should the conditions alter. i.e change in temp/pressure etc This could give rise to a sufficient amount of water in the fuel lines to cause power loss or complete shut down.
Leaving an aircraft overnight in conditions where daytime temps are in high 30degs plus and night temps drop substantially can cause such a problem.
Daily sump testing and checking fuel supplies before and after delivery are essential for longevity..........