Looking at that video and another from the same people it looks as if the tank is in two parts, the little one you see from inside the bonnet and a much larger one underneath. The 'hole' you can see through the filler is the connection between the two, either the bottom half has come adrift from the top or the seal between the two has gone. If all the water you pour in the top comes out under the car then it sounds like they have come adrift, if it's only some of it then you may be able to pour enough in to fill the bottom and as the pump is in the bottom section it 'should' still work.