In case this is of any use to anyone I've just found out why I had 2" deep water in the rear passenger foot well.

First thought was that someone had spilt a drink. Second that it was related to the screen wash stopping working, see below. Third that it was due to leaking roof / bars. Turns out it was none of these and I've had to apologise to the family for ranting about having drinks in the back.

I've taken the carpets out to dry them. There was probably a gallon of water total soaked into the sound insulation under the carpet. Getting the carpet out required taking the drivers seat out as well as a fair amount of trim around the rear door etc. BTW I chose to not unplug the seat harness - I read in a technical bulletin that the yaw sensor is mounted on the seat and requires re-calibration if replaced - I'd prefer to avoid compounding the problems.

Cause appears to have been that the EEC drain had become detached from its hole in the bodywork. I found this under the carpet on the side of the centre console on drivers side (UK spec. car). To check that this was the problem I ran the ECC full. It's pretty surprising just how much water goes through this drain, probably of the order of 2cc / minute. The hose has a rubber grommet at the end which is meant to hold it into the hole, but neither this or the extra bit of tape that was there appeared to be working. The drain had been discharging water into the front carpet and from here right through to the back of the car. Incidentally the carpets appear to have a waterproof membrane between the carpet side and the insulation layer. This was why the water had not been seen in the front before the puddle in the back got to be big enough for goldfish.

Anyway, with the carpets almost dry I'm off to put everything back together...

I now have three more problems to fix, in case anyone has any advice:

The windscreen washer has stopped working. Tank is full, pump makes the right noises but nothing comes out on either the windscreen or tailgate. I've tried taking the hosing apart at the joints under the bonnet, the nozzles are not blocked and no water makes it to the joint. Any ideas?

My horn has stopped working. Haven't yet tried the alarm to see whether it is the sounder, but pressing the steering wheel has no effect. Again, any ideas?

The final one sounds expensive... Every so often when I try to start the car the starter motor fails to engage and just spins. Sometimes when starting normally it gives a little chirp just as the engine catches. I suspect that I've got a damaged flywheel with at least a tooth missing. Can anyone think of any other cause?

Inspite of all this I still think that my 2004 V50 T5 is a great car.

Copious amounts of water in the rear passenger foot well --
My husband and I have had the very same problem with our 2005 V50 station wagon. We, too, had to apologize to a family member whom we'd accused of leaving the car in the rain with a window open. We've been told by the Volvo dealership that we need to change the air filter and empty the drain pan ourselves although we have an extended warranty -- so the vehicle is definitely under warranty. Any suggestions? Anyone else with this issue?

Sorry to hear that I wasn't the only on Phays...

I hope that you do manage to get your dealer to rectify this for you. There's more work to do than I'd be able to afford at dealer rates here.

The insulation forms a very large sponge under the carpet. I wouldn't expect it to be possible to dry this out properly without a few days with the car stripped down. My only piece of advice would be to make sure that they don't fix it too quickly.

Best of luck!