street-washer

from The Century Dictionary.

• noun A faucet or tap on the outside of a dwelling or just inside its street-wall, to which a hose may be attached for washing the sidewalks or watering the roadway.
• noun A cart or tank on wheels carrying a supply of water, which can be wheeled to desired parts of the street and there used for cleaning the pavement. In many forms the water is forced from a closed tank by means of air-pressure in order that it may flow with greater velocity from the nozles and remove dirt more effectively. It is used on asphalt, brick, or other impervious pavements.