What is back-flow?

Backflow is any unwanted flow of used or nonpotable water, or other substances from any domestic, industrial, or institutional piping system back into the potable water distribution system. The direction of flow under these conditions is opposite to that of normal flow and is caused by either back-siphonage or back-pressure:

  1. Back-siphonage is backflow caused by a negative pressure (vacuum or partial vacuum) in the supply piping. Backsiphonage occurs when system pressure is reduced below atmospheric pressure. The effect is similar to sipping water through a straw.
  2. Back-pressure is backflow caused by pressure in the customer’s plumbing being greater than the pressure in the water supply piping. The higher pressure in the customer’s plumbing may be from a booster pump, heating boiler, etc.

Sources of Backflow

Outside water taps and garden hoses tend to be the most common sources of cross connection contamination at home. The garden hose creates a hazard when submerged in a swimming pool or when attached to a chemical sprayer for weed control. Garden hoses that are left lying on the ground may be contaminated by fertilizers, cesspools, or garden chemicals.

Preventative Measures

The Abington/Rockland Joint Water Works is continuously jeopardized by cross connections unless appropriate valves, known as backflow prevention devices, are installed and maintained. We continually survey all industrial, commercial and institutional facilities in Abington and Rockland to make sure all potential cross connections have been identified and eliminated or properly protected by a backflow prevention device. We also inspect and test each backflow preventer to make sure that it is providing maximum protection.


For additional information please see the following websites:

Contact Us

Please call this office at 781-878-0901 should you have any questions regarding cross connections and backflow.

Show All Answers

1. What are the current water rates and charges?
2. What is a cross connection?
3. What is back-flow?
4. How can I save water?