I would check 3 things
If you have water jets to clean your main lights check the pipe for that as mine has gone manky and started leaking, you can take out the fog light and have a look in there for a leak point.
If you don't see anything then you can easily jack up the car, undo the 6 screws that fix the bumper to the plastic under tray and you can flex the bumper and have a look at the bottom of the tank.
On mine you can only see half of the tank from either way.
Also if it's a leak from the pipes connecting to the windows you may want to check to see if you still get pressure to the water jets on the windscreen as that pipe may of fallen off.
How quick does it empty the tank we talking seconds or hours?
Cheers