I was just wondering if anyone would have any ideas.... I have a 2007 focus ST. A couple of days ago getting my son in the back seat I noticed a small lake in the footwell, behind the front passenger seat. Has anyone any ideas what this could be? Was hoping to avoid a massive garage fee if possible 

3 door or 5 door ST?

If it's 3dr, we can rule out the rear door seal...

Either way, I'd start by checking the boot on that side first.  If that's dry, check the front footwell.  If that's also dry, we've quickly narrowed it down to just the NSR seat area.  

This is a common fault on the ecoboost and it may well have the same issue. There is a sealed compartment on the rear quarters with vents behind the rear bumper/Valence, this has to be removed to reseal around the vents, water runs in here, fill the compartments untill they over flow through a convenient hole into the car. Quick fix, underneath the rear quarters you will find a rubber bung, pull them out to drain. If it is indeed the same issue as I had

9 hours ago, jordancann said:

I was just wondering if anyone would have any ideas.... I have a 2007 focus ST. A couple of days ago getting my son in the back seat I noticed a small lake in the footwell, behind the front passenger seat. Has anyone any ideas what this could be? Was hoping to avoid a massive garage fee if possible 

Most likely be the roof rails, under the plastic trim is where the roof meets the body, over time the sealant cracks and unfortunately water gets in, also check the rear boot hinge  recess area as the sealant can crack there too, not uncommon either is the rear light fixing points the little black seal under the nylon bush perishes and lets water in too.