Where is the leak?

[mush145]

The spare space behind the passenger seat keeps filling with water (the area you could put a second battery) It seems like it is completed sealed so I am struggling to work out where the water is coming from. I needed to find out where the water is coming from so I can put a second battery in the space but do not fancy this with the water.

All help greatly appreciated

[Mocki]

it will be coming from the wheel arch, look for a small hole been drill by prev owner, or if you are really unlucky a rust hole, or poss from the bolt that holds the breather tank in the wheel arch???