Hi, 

I recently bought a 2010 fiesta and was frustrated to find the usual water leak in the boot on the right side of the car.  Needless to say it results in wet boot carpets and when I took up the back seat there was water there too.  I even checked the rear and front carpets on the drivers side and was annoyed to find that they were wet underneath, especially the rear one, and spent the last two days drying them out.  
Anyway, I saw on here it leaks from various places on the rear through various seams so I got some rubber sealer yesterday and managed to seal the upper joints on the drivers side, under the roof gutter, seams and boot hinge, and intend to remove the rear light soon as the inside of the lamp is damp, so there must be water getting past the rubber seal too. 
But, I just checked the tea towels I had stuffed in the corner of my boot to absorb the water, which are usually sopping wet after any rain, only to find that they are dry after hours of heavy rain today, so I am well happy 😊.  I will still keep going and seal the other side and under the lamps just in case but I’m still happy.  
So, if your car is the same try sealing the rear especially under the roof gutter which is where I think my water was getting in.  

Roof gutter was where the leak was on my 2009 Fiesta - well done on having a go yourself, and I'm not being patronising because you have a female username; I'd say the same to anyone.

So many people won't try in the first place.  I look forward to your post on successfully changing your brake-pads in a few months 😊

lol.  Think that’s a little beyond me 😂.  

update on the water - I checked the towels again and there is a little water still getting in, not a lot and far far less than before, so it must be coming in from behind the light.  

Pictures of the moisture in the light cluster and the sealing of the gaps on the drivers side.  Passenger side to be done when dry.