This image shows a cinder block wall that a competitor washed using a cold water machine and instead of cleaning it uniformly they skipped around ruining the wall and making it rough. It is important to be aware of how the cleaning company will clean an area and to make sure that they are using the correct pressure and temperature so they do not ruin the surface.
When using hot water machines with chemicals you are able to use the heat to break down what is being cleaned. When using cold water you are relying solely on water pressure, and this water pressure can ruin surfaces costing hundreds of dollars to fix.
you should also be aware that new laws mandate that companies performing cleaning operations capture and dispose of waste water in an approved fashion. Cleaning companies that allow waste water to end up in storm drains subject themselves, the property managers and the building owner or home owner to a $10 000 a day fine plus the cost of clean up from the storm drain, bay or ocean if necessary.