Recommend me a water purifier for cleaning my car

[graeme4130]

Can anyone recommend a reasonably priced decent water softener that works inline with a garden hose for cleaning my car.
My TVR seems to show the water marks much worse than my other cars and invariably, I always miss little bits with the squeegee and chamois when cleaning and end of with little White marks everywhere
Anyone on here use one of these products and do they actually make the car dry without a trace of the water ?
Any advice would he greatly appreciated
Cheers
Graeme

[richardxjr]

I use (hard) tap water, but dry with a microfibre towel. No marks.

[RobCrezz]

I find just drying it with a microfibre cloth and some detailing spray gets rid of any watermarks.