C. Charles Hahn said:
We can't have a discussion about whether a gas station tunnel wash or a waterless wash is safer for a car's paint?
Personally, my thought would be this: in the best case, a waterless wash is safer and likely more effective since it is performed manually (meaning the operator can make sure they don't "miss a spot" like an automated tunnel wash might, and they can regulate exactly how much pressure is being applied to the wash media). In the worst case a waterless wash may be impractical (dealing with large mud deposits, etc.) but still it is probably safer than a rough brush that may have trapped abrasive particles and/or may be made of abrasive materials themselves.