Yeah Uhmmm, that is not the way water separating filters work.
At best, the best fuel filters on the market filter particulates (aka crap) down to 10 microns. I don't know for sure, but I don't believe even the Merc filter elements are 10 micron. If I had to make a bet they are probably 40 to 50 micron filters.
Either way. The diameter 1 molecule of water is 3 Angstroms. (Angstrom being A for short from now on) 1 A is equal to 0.0001 of 1 micron. For a paper filter to actually filter water. It would have to filter down to 0.0002 A (as 0.0003 A and higher would allow water molecules to pass.) At the same time, 1 molecule of gas, depending on the blend, averages between 25 to 30 A. So if a filter actually could filter water out, it would not allow gas to flow either. That is why water weighs more per pound than gasoline does. The molecules are smaller, allowing them to bond more tightly together, with less space between them.
Liquids in the fuel system on the filter side are under suction. And liquids flow through that fuel line at a certain speed. The way water separating filters work. And what they do. Is they act as a buffer, and that buffer slows down the velocity of liquids flowing through them, and they allow gravity to separate and tug on the heavier liquids (water) from the lighter fluids (Gas). The paper element catches the crap in the fuel. The acting like a buffer, and allowing gravity to pull water out of the fuel, is a function of the capacity and to a degree more importantly, depth of the filter. Depth isn't just a measure of capacity, it allows the filter to work better and filter more water as a percentage (The deeper they are the better they work) If by happenstance gas weighed more than water, fuel/water filters would not work.
In the case of the cool fuel module. You remove the top cap. Then you remove the filter element. And then you remove filter cup. Any water in the system sits there in the filter cup, not the actual filter element.
As far as adding an additional FW filter before the CF module goes. It comes down to how much vacuum gets built up in the system. All filters create a restriction in the fuel system. Restriction can be measured in vacuum, inches of mercury. Mercury likes to see no more than 4 in/hg. If one were to ask "if" you could add an extra filter, the only way to know that is to measure your existing vacuum, install the new filter, and measure it again. If your fuel tank is below the level of the engine, if you are not running antisiphon valves, chances are you can get away with it. Other than that, your playing with fire. To much restriction leads to low fuel pressure. Low fuel pressure leads to a lean running condition. Lean melts holes in the centers of pistons. The idea of adding extra fuel pumps to the system should not be done by the average boater. There is to much at stake to make it both legal, and more importantly safe.
