I wouldn’t use a pressure washer on my cars because years ago the BMW dealer used one and peeled the paint off my wheels (on two cars!). So I’m wary. But the foam cannon and such is common among detailers, so perhaps I should reconsider.
On cars I care about, I use ONR, a spray bottle, and two buckets. On other cars, occasional hose off or car wash. I bought a gallon of ONR over a decade ago and its still going strong. One capful in the wash bucket is enough. I started doing this when living in a condo with very limited water access and driving a Porsche that I didn’t want car wash scratches on. A good wash consumes 3 gallons of water plus whatever to wash my towels and sponge in the laundry.
ONR Video:
I use two gallons in the wash bucket and a second bucket with one gallon of water only to rinse the sponge. That keeps the wash water cleaner.