Hopefully i can help..
If its certainly rain water then and not coolant from the heater matrix...The next stage really with problems like you have is to establish where the entry point the waters getting in......But first check the drain area under/below the windscreen just to be sure that clear,this is the area under scuttle plastic panel,drain chamber below the wipers..if thats backing up then it can allow water to enter the cars front foot wells.so maybe check that ...As you know the only areas usually that can cause this is either a problem with the rubber door seal strip so you would need to carefully check both on both doors on the side of the car and see if you can spot any small tears or damage especially around the top edge where the roof or where the door meets aswell as along the bottom -
Also too check the both doors drain holes are fully clear they are located under the door along the edge with thin flat head screwdriver just poke up in there and ensure they are clear -
Another likely cause could be door membrane is leaking. this is like a sheet plastic liner bonded behind the door panel, doors will always have some rain water run inside them getting in via the rubber seal around the glass and should drain away via the drain holes at the bottom of the door, if this membrane or sealant fails or has been damaged due to previous repair then water can come through in to the car from behind the interior door trim .to check those the door panel will need to come off so again something to bear in mind - You should also check areas in the boot for example the tail light gaskets aswell as the boot trim too..also ensure the boot area is dry too..
One test you can try is the water hose test . that about the only test you can do really for problems like this - after drying - partially cover the whole area floor with newspaper/talcum powder which ever around that area to help highlight to point of entry etc as any leak into the car will be spotted on the paper etc and give you rough idea as to direction the leak is coming from or coming in even - Then with all windows and doors shut and with somebody else inside to monitor around in the car - pour water either with a garden hose in specific areas - checking one area at a time starting from the bottom up in regards ***** ***** door seems / the lower edge of the both windows / windscreen etc until of course you do stop the water or drips coming in..and se whats found - the problem with such faults as this is they can be quite time consuming trace down and sometimes may involve having to remove inner trim/carpet sections etc to trace it down.But if you havent done so already try the water test and see if that highlights the area the waters getting in.I do hope this helps..