Vehicle Washing
Personal vehicles may be washed at home using a hose with positive shut-off nozzle. However, the Water District recommends use of a commercial or self-serve car wash where water is captured to the sanitary sewer, which allows for recycling. Or, use a high-pressure, low-volume sprayer to maximize water savings.
I think what they're saying here is that washing your car at the self-service car wash is preferred because the wastewater goes to the sanitary sewer system where it is treated and recycled in Las Vegas as irrigation water. The self service car wash spray water is still potable water, its just that the waste is treated and beneficially re-used for irrigation, rather than flowing down the street curb.