According to the Pollution Prevention Act (PPA) of 1990 the term pollution prevention (P2) means source reduction and other practices that reduce/eliminate pollution creation through more efficient use of resources (raw materials, energy, water) or conservation of natural resources. This definition addresses both resource use (inputs) and resource loss (outputs) from various processes.

PPA specified a hierarchy in reference to pollution:

• Prevent or reduce at the source whenever feasible
• If unpreventable, recycle in an environmentally safe manner whenever feasible
• If unpreventable or unrecyclable, treat in an environmentally safe manner whenever feasible
• Use disposal or other release only as a last resort in an environmentally safe manner

Practices that can result in source reduction include equipment/technology modifications, process/procedure modifications, product reformulation/redesign, raw materials substitution, leak and spill prevention, and improvements in housekeeping, ...