Hi
Are you really going to set up a professional car valeting business with a £100 pressure washer? (if I was going to be sarcastic I might suggest you stick your finger over the end of a hose pipe and save yourself the £100! - but I'm not like that)
All you can get for £100 is a small domestic electric machine which would be entirely unsuitable for what you need. How are you going to power it? You will either need to use your customers electricity supply (not very practical or professional) or you'll need to buy a generator which is likely to cost another few hundred pounds (and which you could put towards a commercial machine).
I do know people who have started with (and moved on quite quickly from) a cheap and cheerful domestic machine just to get them going but if it was me I'd want the right machine from the start. Buying anything else will just mean you spend much more time doing the job and will make you uncompetitive.
To answer your question though, pretty much any machine will draw it's own water if it can be gravity fed (ie the level of the pressure washer is lower than the water supply)
The electric is the big problem.......
Here is our range of machines:
http://www.express-cleaning-supplies.co.uk/oos/pressurewashers/551000.htmlRegards
Mike
