water leaking in battery well

[dads taxi]

Hi, new to the forum.
B200Cdi 2006
After hearing 'sloshing' water noises in the cabin during cornering ,finally I have found water in the battery/fuse well under the floor. Anyone any ideas how it got there? Try to regularly clean out wiper area drainage vents so its all a bit of a mystery?

 

[dads taxi]

To continue this post I have discovered that I have blocked drainage in the front of windscreen area, water is leaking into battery well, I have unblocked all the visible grilles at the base of windscreen area when bonnet is open, there must be a drain from inside this the area which i cannot locate?
Can anyone advise or had similar experience?