Can rain wash a vehicle? Why yes indeed it can. The force of a good rainstorm has been known to rinse off stubborn pollen, stuck on bugs, and even bring a bit of shine back to that old, weathered paint. However, you're not going to be able to get off heavy road grime from the rain alone, so if you want to combine the best of both worlds, you can hand wash your car during a good sprinkle for maximum benefit.
Use a good biodegradable car wash product that is phosphate-free, or you can mix up your own brew using a few teaspoons of Seventh Generation Natural Dish Liquid. Start by putting on a swimsuit, give your vehicle a good rub down with the soap and a sponge, then let the rain do the rinsing-off for you. Have the bucket, solution, and sponge waiting by the door to make the most of a quick burst of Mother Nature's generosity.