i got recommended by guys in macquarie 4x4 to put 2micron post filter instead of pre filters.
since d40 do come with water seperator warning sensor. in the event that stock filter serses water there is post filter to back it up. he said he hasnt seen any pump fail due to having extra filter. however he seen countless times pump injector fail due to contamination fuel.
same time i was told by my work collegue that fuel contamination damage can be covered by insurance as well. depends on ur insurance company. i did find that my insurance do cover fuel contamination damage. he said majority fuel station do cover you if your car happens do get damage also in the event of filling it up from rural areas, carry mr funnel (water seperator filter) and check first 10L of fuel and last 5L of fuel going into tank. same for fuels from jerry cans.
They have been running that sort of water trap as stock for as long as i can remember and they have never really worked that well, if they do work they will only send a signal once the float inside the unit has reached the very top, MEANING the unit has to be FULL of water. they never come on as soon as water reaches the unit and that is the problem , its too late by then with the common Rail engine.
My old ln106 Hilux was fitted with one from new and yes at times it has collected a bit of water but never has the light come on, i still keep plugging the wires into the bottom of it after each service in the HOPE it may work, BUT only because it makes me feel better.
In all reality its probably lulling me and other people into a false sense of security thinking it will tell you when it has water in it.
At best i have only ever seen it work once in my old D22, BUT again the signal didnt come on until the unit was FULL of water.
personally i like a clear bowl so as you can have a quick look each time you fill up, or at any time you are a bit worried about the location you bought fuel from. That way you can see if you have accumulated any moisture.
At least then you will be able to tell what fuel station the water is coming from if you are unlucky enough to pick some up which may help in them footing the bill if you do sustain damage.
Also it doesnt really matter how FINE the filter is as water will go through no matter how fine the filter is. The main thing is to get an effective water TRAP not a water filter.
Clean water is still going to stuff your fuel system
I
have just been watching video from "mr funnel" and apparently water can NOT go through filters finer then 5 microns.............. what i dont understand is why it gets through our standard filters when they are SUPPOSED to be 4 microns.
Im thinking it must be due to the fact that the fuel and water if any are being pumped at high pressure forcing it through as apposed to the water trap funnel which obviously is just gravity 
