1. The backing up of water through a conduit or channel in the direction opposite to normal flow.
  2. The undesirable flow of water from a plumbing system back into the community potable water supply.
  3. A reverse flow condition created by a difference in water pressures that causes water to flow back into the distribution pipes of a drinking water supply from any source other than the intended one. Backflow prevention assemblies prevent contamination and are required by city and state laws.