C30 (2010) water in passenger rear footwell
 

Ive just sucked over 2 litres of waters from the passenger rear footwell with a wet and dry hoover,my local garage had it in earlier on the year and couldn't find any leaks by pouring a hose over the car, may take it to a bodyshop but any ideas please as it keeps happening in severe rain

Have a look at this thread. https://www.volvoforums.org.uk/showthread.php?t=299687

Even if you sucked the water out the foam under the carpet will still be soaking wet. The carpet will have to be lifted to dry it out properly.

Do you have a sunroof or not?

I feel your pain, my C30 had a leaking windscreen which led to gallons of water having to be drained from the carpets. There is between 2 and 4 inches of foam insulation under the carpet itself which acts like a giant sponge, took a full week out in the sun to dry mine out!

There are normally 3 possibilities here.
1) Front windscreen bonding has gone allowing water in. If its the original screen, volvo will rebond it FOC. But if the screen breaks, they wont replace it FOC.
2) Sunroof drains in A pillar have become blocked.
3) Aircon drain has become blocked. On RHD cars its immedately to the left in the drivers footwell, behind the carpet.

Had this on V50 estate 2008 rear drivers side.

Found that water (rain) was dripping over the trim over the internal base of door frame. Initial thoughts were the bottom door drain holes plugged up and door was filling up, but all clear. Removed the door card and found the speaker wiring loom was also wet. There are 10 (or so) 8mm bolts holding the door plate on, looking at the nearest side to the hinge (where the loom is) I could see traces of water runs from the lower set. Also across the base of the plate the foam seal was also wet.

After removing the 8mm bolts the plate will have slight play, I moved it upward and ran a bead of silicon from half way up, round the base and half way back up toward the door latch. After reseating the plate and locating on the top 3 bolts the lower bolts also had a shot of silicon into the bolt holes before refitting, this cured my water issue...

Some won't like my fix, but its a work horse not a pride and joy and as it was hidden behind the door card no one will see it.