I don’t think it’s a huge deal as much as people watering their lawns.
I wash my car when it gets quite dirty. Maybe once or twice a month. Spray water to wet it down, use a bucket with a wash mitt and soapy water to actually wash it, then rinse it off.
The water isn’t running continually. Maybe 5-10 min tops through a sprayer which also reduces the flow besides spreading the stream.
If washing a car like that I see no issue.
Contrast that with someone who waters their lawn a few times a week for an hour or so.
I’m sure that water metering will come here and it will reduce usage as people begin to pay for something which is generally free and unlimited right now.