Since 1972, the EPA's Clean Water Act has prohibited the discharge of any pollutant to waters of the United States . Each state and municipal regulatory requirements pertaining to stormwater is based upon this federal regulation with additional provisions to address specific needs and conditions of watersheds within a region.

Portable or mobile power washing, creates wash water (wastewater). Even in instances where only water is used, the wash runoff can contain hazardous chemicals and substances that are harmful to the environment. Washing vehicles and equipment in areas where wastewater flows onto impervious surfaces, such as on concrete and asphalt paved areas, can cause the wastewater to flow into storm drains. Some storm drain systems discharge untreated water directly to creeks, rivers, lakes, and wetlands.

Discharging power wash wastewater into this type of storm drain system is the same as discharging wastewater directly into a water body. State and federal regulations (specifically The Clean Water Act 40 CFR) are enforced to eliminate this form and other forms of water pollution.

Wastewater can contain high concentrations of oil and grease, detergents that may contain phosphates and suspended solids. Detergents, even biodegradable detergents, can be poisonous to fish. Phosphates, an ingredient in some detergents, are plant nutrients that can cause the excessive growth of nuisance plants when the phosphates enter lakes and streams. Wastewater can also contain dirt and pollutants from vehicles and equipment washing.