Roof cleaning processes and associated systems are disclosed. A representative process includes dispensing a cleaning fluid on the roof, at least restricting the cleaning fluid from exiting the roof via a roof drain, and collecting the cleaning fluid from the roof and directing the cleaning fluid to a sanitary sewer. A representative system includes a pump coupleable to a source of water and configured to pressurize the water, a surface cleaner coupled to the pump with a water line to receive pressurized water, a vacuum source coupled to the surface cleaner with a vacuum line to remove wastewater produced by the surface cleaner, and a retainer configured to be removably attached to a building at least proximate to a roof of the building, the retainer being removably coupleable to the vacuum line and the water line to at least restrict movement of the vacuum line and the water line.