re: not re-inventing the wheel,
IMO hot water is one step to far for me , most of you are one man bands and want to tinker with your systems and make your working day easier and more interesting , i cant blame you for that and if i was out every day on the tools i would probably also want to take my system to the next stage and install a boiler. However for me cold water works and works well and i have 4 vans going out every day with cold water, over 2000 happy customers (well most of them are happy anyway) that get their windows cleaned with cold water. Like i said for me adding anything to this already succesful formula is pointless for me , maybe not for some of you though. I get your point about TRAD vs WFP etc however we are not talking about a change in working practices as great as this and all the benefits this brings.
What we are really discussing is
PRO
the windows may get cleaned quicker using hot water
easier for vans to thaw on frosty mornings
CONS
more expense (initial and ongoing)
logistical headaches in installing a boiler
more to go wrong
extra responsibility re dangers of using gas (especially if you have staff)
making a good and simple money making machine more comlicated than it needs to be.
Like i said for me hot water is not a good advance for my business and i wont be doing it.