Citroen C4 water in air vents

Very common and usually caused by blocked bulkhead / scuttle drains being blocked . This explains

" Hi there, it's hard to get access to the drainage holes in the bulkhead from above. The easiest way to get at them is to remove the front wheels and remove the wheel arch liner behind the wheel. Now you'll be able to clean out the drain and run the hose through the scuttle panel to clean out any other debris
This will cure your water leak inside but you will need to have a look at your interior blower fan as the water leak runs through the motor and causes it to burn out. I've had quite a few with water leaks and the blower fan burning out "