Black streaks (Under Window)

If the black streaks are on your window leaving like a hard residue that seems impossible to get off, then you need to compound the glass. Yes, using a rubbing compound something like Meguiars M100 Pro Speed Compound or similar will remove this and will not scratch the glass. Follow through with a polish and then simply clean the glass like you would normally.

In the future, you'll need to find way for the water to run away from the glass to prevent this from happening again. You can also try using Rejex paint sealant on the glass as well which will also help the glass.