A quick search using “ water ingress “ threw these up, maybe worth a look. I’m pretty sure that if you change the key words you’ll get a few more results as I’m sure that this topic comes and goes every so often.
This from armoore.
Is the heater matrix U/S as implied? If so get it replaced, not easy OR:-
Remove plastic shroud at the lower edge of the windscreen, passenger side, inspect plastic cover over the air intake for ventilation. See if the sealant at the upper edge of this cover is in good condition and replace with RTV sealant if not. This can cause ingress of water into footwell. Do not taste the water in the footwell to see if it contains anti-freeze, get someone else to do it!