Until now I have experienced two kinds of water leakage in my Rover 75. One of them is (supposedly) causing a failure of the fuel pump power output, so 99% of the times the fuel pumps (both under bonnet and in tank) receive no power and the car isn’t able to start; this leakage is due to the water piling up in a small “pool” right above the BCU and the internal fusebox, where a rubber drain is supposed to prevent this occurence, but fails to do that if you live someplace where leaves and seeds from the trees fall on your car.
The other drain, I discovered by pure chance. As I said, I investigated the first drain after the pumps failed to start, so I thought the pumps actually failed; I went and checked the in-tank pump, by pulling out the back seat; behold the surprise, there was another quite big pool of water in the recessed space close to the in-tank pump housing cover. I was able to trace the water stains up to the trunk, close to the rear lights; it was difficult to find the cause because everything was mostly dry, but I noticed a slight running water stain.
I generously added silicone to the gasket area, both from outside and inside, and put everything back together, should be pretty much isolated by now. For the sake of it, I did the same treatment for all the accessible gaskets of the silver lining (there are two on both sides).
My no-power-to-fuel-pumps problem is not yet solved though, this car likes to play games, and when I see the pumps are working again, soon after, at the next engine start, they aren’t anymore. At this point, I suspect a faulty wire.