I would look into the CR Spotless systems. Little pricey but worth it to spray your car off after washing then walk away. I have three black vehicle and a dark grey one. Nice system to have for dark vehicles.
And CR Spotless has a resin exchange program so it's really cheap and easy to replace your 'fitler.'
I recently got the CR Spotless twin cylinder for use on my black Trailblazer. I was not really confident it would do all that they claimed...but was pleasantly surprised. The secret (not really, they tell you to use one on their site) is to run it through a pressure washer to get water consumption below 2.0 GPM. Since I didn't like the idea of my gas pressure washer running while washing, I opted for a inexpensive Karcher electric unit off Amazon. 1.8GPM, runs only on demand, and was about $100.00. I have used it probably 4 times, both indoors and out with ZERO water spots. Just a note, If you allow vehicle to dry outdoors, you will see some spotting, but it is just dirt, pollen, etc. that can be easily removed with some detail spray. Would be great for campers, RVs, tractors, and even for washing windows. I guess anything difficult to towel dry.