I can't answer specifically for the X Trail but I have driven a Land Cruiser through water at bonnet level in Africa & the only modification was a fitted snorkel.

Driving through deep water is very much a skill to keep the bow wave pushing out in front of you & a dry void in the engine compartment.
Too fast you swamp the engine because you catch the bow wave up.!
Too slow & the bow wave collapses back over the bonnet & water can fill the engine compartment.

Always walk the route / crossing first to ensure there are no surprise on the river bed this guy didn't!!.

 

Wading depth for the T30 is 53 cm and the T31 is 35cm anything over and water will get into your rear diff through the breather pipe.

 

@Umbong: thanks. But now I wonder why some X-ies drive through water as deep as the doorhandles (so to speak). Do they use extenders or so? I see Jeeps go completely under till the front window... I know about air intakes till the rooftop, about exhaust pipe extenders too. But the rest? Electricity? But on the other hand, it's not a specific terrain vehicle...

 

Wading depth for the T30 is 53 cm and the T31 is 35cm anything over and water will get into your rear diff through the breather pipe.

I don't intend to do any wading, but who knows at the moment. Is there anything that can be done about the 35cm limit on the rear diff?
I know LRs you can buy all sorts of breather kits, but probably not for the T31.

 

You could extend the breather pipes, there are kits available to do so, though it is not rocket surgery, the problem is where ? I would think the rear axle could be taken up in to the rear pillar, and you would probably be ok, but this would require further investigation.

The problem as I see it would be the front ones, you could extent them to the bottom of the A pillar without to much worry, in effect top of bonnet height. Some off road vehicle owners like "GOJeep" have come up with alternative solutions for the air intake too. http://www.go.jeep-xj.info/Exterior.htm - See Air intake diversion hose.

After that where too ? On Raised Air Intakes I fitted to other vehicles I would normally fit the breather tubes out side following the RAI or "Snorkel" up. So next question is where to get a snorkel ? :biggrin:

 

If you wanna use a snorkel, you must go through the fender and inside panel. All the pipes, connections and fittings need to be watertight. Do not know if they sell em. But do you wanna go that far? Personal, if I wanna wade that deep, I would buy a car who can...