If you are talking about washing cars using a brush with pure water fine for a couple of quid a car.
if you are talking about valeting cars for £50+ then no not suitable at all.
the pure water aspect is fine, but you just can't use a brush on the paintwork it will finely scratch and damage the paintwork causing swirling, in much the same way that a car wash does - which is why people who care for their cars use a valeting service in the first place...