There is a known Ford bulletin regarding water in footwells (usually NS if RHD car)
It is caused by the Pollen Filter Air Plenum (plastic box flush with NS of scuttle trim) It is often knackered by servicing mechanice taking off the cover (parts on it break off) which leaves you needing a cover. The plenum seal leaks and goes into the car.
I used to have a copy of bulletin .. not any more, sorry.
If you can't find any other reason, check with Ford dealer and ask if you can read the Focus Heater Plenum leaking into footwell TSB.