Having the same problem man... Was living in an apartment complex and had no option but to keep the car outside. It got rained on and the sprinkler system in the complex always hit the one side of the car in the morning, leaving the sun to dry off the side (and leaving spots all up and down the side and on the roof). Washing it just doesn't do the trick, and sometimes seems to make it worse!
Gonna try that chemical guys product to see if it works.
'11 BMW E92 ///M3 - ZCP and DCT
'15 Ford F-250 - Lariat, 6.7 Powerstroke Turbo-diesel