1. the flowing back of a liquid, gas, or other substance in a direction opposite to its normal flow
2. the unwanted reversal of water flow in plumbing systems
Usage: plumbing; technical

Examples

• The backflow of sewage into the clean water supply created a health hazard.
• A backflow preventer was installed to protect the drinking water system.
• The plumber checked for any backflow in the irrigation system.
• Heavy rains caused a backflow of water into the basement.
• The backflow valve automatically closes when pressure drops.
• City regulations require backflow testing for commercial buildings.