Similar
problem over on the driver's side footwell water puddles in our 2009 Seat Alhambra. Same design as the Sharan and Galaxy where the windscreen water channel drains out into the wings via rectangular holes. Thanks to another member's guidance, we removed the plastic wheel arch liners and went looking for and found 2 small holes DIRECTLY UNDERNEATH the drain outlet. Best guess is that under certain conditions water tracks down from the drain outlet, into the hole(s) and then down towards the brake booster pump. The puddles in the drivers footwell start on the bulkhead directly under the brake pedal. We've taped over the holes with waterproof tape so fingers crossed that will solve the
problem. There was another hole closer to the A-pillar (door hinges) but away from the drain outlet - this had a factory tape over it which was peeling off. Unlikely to be the culprit, but retaped it anyway. Seems likely that the first 2 holes mentioned should have also been sealed over, but that the tape/wax/rubber bung had fallen off over the years. For members with the water leaking on the passenger side, might be worth checking just below the drainage hole in the wheelarch and seeing if there are any open holes below it.
On a related topic - the rear screen washer pipe - the washer on our car had failed and we tracked down the breakage not to the connections in the passenger side footwell, but in the tailgate hinge area. There is a flexible black rubber tube at the top left (passenger side) inside of which runs only the tailgate washer pipe. The factory had fitted a corrugated plastic flexible pipe which had turned brittle and snapped resulting in water squirting inside the rear C-pillar instead of onto the screen. Reconnected with a joint connector and working again.