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What is backflow?

Backflow is the undesirable reversal of the normal flow of water or other liquids, mixtures, or substances into the drinking water supply.

This occurs in two ways.

  1. Backsiphonage: When a drop in Fairfax Water’s supply pressure creates a suction effect drawing water out of a building, house, or other private plumbing system back into the Fairfax Water potable water system. Real examples that could lead to decreased supply pressure include opening or closing a valve, flushing a fire hydrant, or a water main break.
  2. Backpressure: When a building, house, or other private plumbing system with greater pressure than Fairfax Water’s supply pressure pushes water from the building, house, or private plumbing system back into the Fairfax Water potable water system. This can occur in a pressurized system with booster pumps, chemical feed pumps, boilers, elevated storage tanks, or recirculating systems.
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Fairfax Water is exempt from Federal, State and local sales and use taxes (ID # 54-6025290)