I have spent a LOT of money on this issue. After a major flood here in New England last year my X3 rear floors were soaked. I pulled up the carpet and pumped out several gallons of water. Called insurance company-to shorten the story a bit-new gasket set on panoramic roof, windshield gasket, door panel gaskets---shall I keep going-new carpets etc!!
All fixed----!! Sorry about midsummer I noticed a strange smell like windshield washer stuff!! I had been noticing that I was refilling that tank often!! Looked under the rear carpets ---you guessed it ---a gallon of the missing windshield washer fluid! I pulled the pimp from the tank and plugged it with a pencil! When I get around to it I'll pull out all the seats and carpet and find the plastic pipe that travels through the passenger compartment and leaks!!!
Thousands of dollars worth of expense and damage---for a plastic hose-leak. Small things can cause big problems-and they are often very hard to discern. The major catastrophes of the world have often been linked to simple parts failing. Airlines exploding –fuel tank pump; Space shuttles exploding, O –ring, Bridges falling down,--one broken rivet!
In the big picture it's only rear window washer not working and a damn wet floor!