There are not a ton of car wash tools that actually save water, but there are methods to conserve water while keeping your car clean. As far as products go, there is a waterless car wash spray that can be used on a moderately dirty car. It is not always necessary to give your car a full wash, so a using a spray can save water. Simply spray on your vehicle and then wipe it off with a microfiber towel. This type of spray gets good ratings from both experts and consumers. As odd as it sounds, using a car wash actually uses less water than doing it at home. It is also more environmentally friendly, because all of the waste-water is sent directly to a water treatment facility.
For more info, see Green Car Wash Tips and Tricks