My first diy guide. So bare with me!
Is your windshield spray in your z4 not working or spraying really weak? If so, follow this guide to fix it. Disclaimer: Do at your own risk although this is really easy and hard to mess anything up.
First you might want to do some checks. Are the fuses okay?(check owners manual on location). When you pull the lever do you hear any winding motor sounds? If not, it most likely the fuse or the motor(13 dollars at oreilys- shown how to replace also below). If it is winding and no spray or weak spray then follow below. The cause of this is most likely built up mildew and dirt in the filter location after the motor. With these direction you'll clean the filter to make a perfect flowing system.
Step 1: Pop open your hood and you should see the windshield fluid reservoir on the left side of the engine bay. You should see the motor pump on the right side of it with a harness coming in. Pull the harness off and wiggle/pull the motor out of the socket inside the reservoir. It really easy. Just pull and remove the harness connector and the tubing. Reverse directions to replace it.
Step 2: After that there is a 1(one) 10mm bolt holding the reservoir in place. Remove that and pull the reservoir out. After doing that use hose and clean out the box. Also at the spot where the pump come out there is a black round rubber thing that holds the filter. Pry that out and there should be a bunch of dirt. Clean it and then put it back. Shown below after mine was cleaned.
Step 3: Reverse all direction above to put it all back and enjoy your newly working spray!