Inviting comments from anyone who's familiar with the anatomy of the driver's side floor channel (the one which runs along the sill and contains the bundles of loom wiring). I emptied mine of water a few days ago, and removed a load of water from the insulation under the driver's side carpet. At the time I figured it had got there courtesy of a disconnected a/c drain during the summer. However, two days later the channel has half filled again (to be fair, it has rained alot)...the door seal's not damaged, that I can see, and no real signs of water around the door. Could the contents of one of the sunroof drains end up in that channel, if one had become dislodged? Is there mean to be a one way valve or something, in that channel, which would allow things to drain?

Tnx for your help....

There's talk about water getting in through the pollen filter housing. Mine is wet like yours after a week in the rain (I normally garage) so will have to investigate as well.

Good thinking, in theory i sealed those up, but worth checking. I shd add that this time it was the channel that was full, but the insulation wasnt really wet, and the carpet was fine. I'll lay down some blue paper and see if i can spot a drip

Sunroof drain could be only from the top area, because after it goes down the A-pillar it exits the cabin - the outlet is in between the fender and the door, you can actually spot it if you open the door.
If blocked on the upper part however, you should have leak spots in the headlining or in the carpet.
On mine I get a drip (little) from the upper seal (roof/door seal), I've silicone it but still does drip (it is glued originally to the roof area, but with the years it lets go, and it also "smashes flat". The rear doors have the same problem... and all those one drip right into the sill channel area.
Hope you find the cause ... water ingress is one of my top hates in a modern car, nevermind a "British" car, and a "luxury" car ... :-(

Pollen filter housing - or a buildup of leaves etc in the drain from the plenum can cause water to seep in aswell.
When sealing up the plenum, I find taking it all apart to the point of unscrewing the pollen filer housing and folding the rubber gasket back to clean under it and running a bead of sealant around there also helps.

I recently sorted water ingress for an owner where the issue was water leaking in from the top of the windscreen (it was factory original!) - there was obviously enough of a gap in the sealant that was allowing water through, where it then ran down the A pillar and into the sill/footwell.

Another location of water ingress onto the floor is through the holes used to hold the lower windshield trim in place. With age the clips that hold that trim in place get brittle and snap off. Also, if your windshield has ever been replaced then these clips in all likelihood have been damaged.
I recently had this problem and ended up buying a new lower windshield trim. I found 5 of the clips damaged and no longer holding the trim to the glass. When ordering this trim you will need to ask seller to include 6 extra clips because they never come with a full set. After I installed mine I ran a thin bead of clear silicone along the upper trim piece between it and the windshield glass. Haven’t had a drop of water since.
Added to this, I pulled the wiring loom you mention out of the sill and drilled three separate holes along the channel so as to allow drainage of any water in the future. I did the same in the floor of the spare wheel storage area as water seemed to gather there a lot. Make sure to protest the bare metal with your favorite product after drilling the holes.....

JMCLuimni wrote:

Another location of water ingress onto the floor is through the holes used to hold the lower windshield trim in place.

That's worth bearing in mind for any work in that area, they break fairly readily - I didn't order enough last time I took that end of the car apart. Opting instead for silicone all round the existing bits. The screws for the covers and bits under that area, where the bonnet hinges down and over - intake plenum cover or something- sit in little plastic things that manage to leak in interesting ways as well. Looked at it again last week and the sealant is showing its age now. That said a combination of cleaning out under the filter housings including their drains and resealing (including replacing the pollen filter covers) did work better than expected.

Martyuk's reply - "Pollen filter housing - or a buildup of leaves etc" sums up the main cause of my leaks, when it DOES leak it can't run away if they're blocked I suppose.

Thanks for the suggestions. I'd sealed up the plenum 6m ago, and the pollen filter was bone dry when i checked it today. For good measure I added a ton more silicone, but it all looked pretty good tbh.
Sunroof drain was fine (exiting behind the wing panel, as noted above). I'll take another look at the door seal as suggested - maybe something is getting in there
BTW My spare wheel well is bone dry these days... I RTVd the top of the upper tailgate seal to the lip it mounts on.

I like the idea of drilling a couple of drain holes. Is there a professional way to finish them... a nice little one-way valve, for example?

Hmm. That's a puzzling one. I've had the rear carpets out of mine for most of the year (back in now) and the front cill plates/covers up a couple of times - the loom routes along the outer sides seem quite dry on mine. Haven't checked the wheel well since I put the boot floor cover back in - I replaced the rear hatch seal and looked at all the usual places as it was filling up regularly (not just condensation, or I don't think it was). The soundproofing was sponge-damp and any leaks vs condensation monitoring quite hard to do. With the soft finishes all out it stayed dry even with a hose on it, but of course it was summer, warm-ish and the floor hatch was off. Will find out how well it copes with Autumn plus carpets back on-board.

I did discover an absence of visible leaks excepting the flaps/vents for air-out at the tailgate top, that had filled up inside the wiper motor casing. After cleaning and replacing it sort-of-properly it doesn't seem to be doing that now.

Mind you, my heater is stuck at full heat, passenger side at the moment (had the dash out and decided that dismantling and cleaning the motor might work - it doesn't, should have done it properly). If that circulates round it might at least help keep the inside dry.