Rubbish idea.
It takes the polish off and loses it's shine.
Just like windows done with wfp, they're flat not shiny.
And yes I do know what I'm talking about.
I'm a fully qualified Autoglym Motor show valeter.
Squeaks, isn't usually right, but he's wrong again.
Remember pure water is like rain water; it's just soft water; not a bleaching agent or a detergent.
Pure-water-cleaning began in the USA, aparantly, and was originally used to rinse cars. It's best used to rinse a car after using a liquid shampoo/polish. Rinse your car with pure water and it dries as if you've dried it with a shammy leather.
I've tried rinsing my car with my WFP, but found that using jug fulls of the stuff does a better job. Your car dries all lovely and shiny with no 'tap water blemishes'.
You can also purchase (Wilkinsons sell them) an aparatus which uses De-ionised water to rinse your car.
So, to conclude, pure water is like rain water; just water with no impurities; it's not a bleach or a detergent and Squeaks is wrong; again.