For an eco-friendly car wash, see if there's a place in your area that uses earth-friendly soaps. If not, consider an at-home wash. But do it smartly. Use a bucket, and keep the hose off as much as possible. And since the water run-off will head straight into the sewer system or nearby water sources, use "green" detergents (some of which are waterless too).
EcoTouch waterless kit