Yes, I found in Huntingdon rain water always left a deep red residue.Where DunnyRail and I live, the rainwater seems to be full either of the Sahara Desert, the Gobi Desert, or the Steppes. When it rains, the detritus left on your car could be gathered up and use to plant desert flowers.
many moons ago I bought a small - 4.5l - desktop distiller unit, as found in many small laboratories. Next time I use it, I'll post you what comes out of our Anglian Water ['love every drop'] pipes, left in the bottom of the tank....
You'll either laff, or be horrified.
I do ALL my locomotive water TWICE.