Mine was doing the samething. I ended up finding out the headlight washer pump was not working and the two o rings in the strainer were missing. Still waiting for the new pump and strainer to arrive however in order to stop the wwf from emptying out every 3 days I took some silicone and put in in the strainer (tried to fill the place where the o rings go) and then put some on the pump. Inserted it and let it dry for 4 hours. No more problem with it leaking. BTW, I checked the headlight hoses by pulling the hose from the pump and taking my small air compressor and blowing some air through the hose to confirm the pumps and everything was fine.

Hope this helps.

__________________
Cheers!
Bill

2002 X5 4.6is
Estoril Blue, born 11/01
~226,000km's
rebuilt tranny (11/12)
New paint (8/12)
Chain rails inspected and are good (01/13)