Pressure washing is an excellent way of removing pollutants from outdoor surfaces. However, pressure washing wastewater should never be discharged to a storm drain. Storm drains should be covered, or the path to the drain should be blocked during pressure washing. With the property owner's permission, the collected wastewater can then be pumped into a sanitary sewer clean out, or, in some instances, discharged to a landscaped area, provided that the discharge does not overflow the landscaped area, contain hazardous constituents, or create nuisance conditions. Sump pumps and wet/dry shop vacuums can be used to pump the wastewater.
BMPs for Pressure Washing and Surface Cleaning booklet for more details.