I am just about ready for final inspection and don't have a gascolator as I have 2 filters (90 and 10 microns) and as for water, the tank drains are my lowest points in the fuel system.
I was going to argue that water can contaminate fuel when refueling if a tank cap is leaking or by condensation with little fuel in tanks. (any other possibilities?)
Neddless to say, tank draining after refueling and before flight is essential.
In a gravity fed system, with time, a gascolator will do its job.
Outside my tanks, in the hoses to/from the engine, fuel is circulating at a (measured) 50 gallons/hour rate and will move any droplets around (if any), and "dilute" them in the fuel.
A gascolator will never catch these "outside the tanks" probable droplets.
On top of that, the supplier of my EFII system does not recommend the use of a gascolator.
In Canada or elsewhere in the world a sound and well thought out fuel system is primordial.
If a gascolator is needed and useful, use it.
Otherwise, other mitigation has to be in place to catch debris and or water.
Thankfully, Transport Canada is acknowledging that this "previous across the boards requirement" don't always have its place in an aircraft.
This thread also covered the not obligatory gascolator issue in Canada