Why does the rainwater sheet together where my windshield wipers have recently passed, but bead together where they haven’t?

Question

[Kind of crappy visual aid](https://i.imgur.com/zrzlYkW.jpeg)

I’m sitting in my car, procrastinating going inside because of the rain, and I noticed that the rainwater is behaving differently depending on the area where the windshield wipers passed and where they haven’t.

Why is that?

In: 91

Answer 1

Wear patterns on the hard-to-see microscopic dirt that’s on the glass. Near the edge it is fallen dirt, and in the wiper pattern, it’s smeared dirt

If you clean the windshield properly, really degrease it, get everything off, maybe even get it a wee polish with glass cleaner, then remove all the products back to only having pure water on it, then dry it and wax it (if you get this done professionally, they’ll call it ‘sealing’ but it’s just wax) then wax off, then you won’t be able to see water collecting anywhere

It’s because water has a ‘sticky’ property to it, where it doesn’t shed as well if it has something to grab onto, it will form beads or a thin surface covering