yes you can offer this service,pure water is fine, it has been using purefied water for many years in america,number one for car wash market,but if you do with brush,would you take hours to finish a 4x4 with 3 kids and 2 dogs, and charge only 25 pounds,plus a big van, and marks everywhere, you know what, if you have a round of window cleaning,stick it,because cars are not like houses, they move,they have accidents,crash,people going on holiday,etc
I do car valeting,but I hope to leave asap.for window cleaning. because long hours,short money...