If I am not going to polish or wax the car - which only gets done every 3 or 4 months - I just don't dry it. Even when I am going to do more than wash it's generally in the summer and the car dries naturally very quickly. I've used de-ionised water to rinse down the car for years now, and whilst there are some light swirls and scratches, the paintwork is in great condition for it's age because the only time I touch the paintwork is with a clean wash mitt.
I use one of these :
https://www.cleaningspot.co.uk/acatalog ... tml#SID=29
A full bottle of resin lasts about 3 or 4 months depending on how often you wash - I only use it on one car, and occasionally on the windows of the house. You get three fills out of a 25kg bag of resin, that's a bag a year at about £84 once you have the kit. All I do is wash, rinse, walk away. Zero water marks until the resin starts to go off, which you can anticipate with a TDS meter - when particulates get to about 5-7 ppm it's time to change.
When the resin is done you need some of this :
https://www.cleaningspot.co.uk/acatalog ... tml#SID=29
You need one of these to re-fill it :
https://www.cleaningspot.co.uk/acatalog ... tml#SID=29
And a cheap TDS meter :
https://www.cleaningspot.co.uk/acatalog ... tml#SID=16
In the summer in particular I used to find myself chasing the water round the car to prevent spots - clean a panel, then dry it, clean another panel, then dry it. Or worse, using a detailing spray at the end to aid drying but also rubbing water marks off. Complete ball-ache, not ace to the paintwork, and time consuming.
I have a friend who is a professional detailer, he'd heard of this but never been convinced. He saw the paintwork on my 12 year old car, bought a set, says it's changed his life
No snake oil here, just completely contaminant-free water, air and sunlight when available