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About Cross Connections
Massachusetts Water Resources Authority

What is a Cross-Connection?

A cross connection is a connection between a drinking water pipe and a water source that is not safe to drink.  The unsafe water can come from your own home.

What is a Residential Cross-Connection?
garden hose
The most common source of residential
cross-connection is a garden hose.  For instance, you're going to spray fertilizer on your lawn. You hook up your hose to the sprayer that contains the fertilizer. If the water pressure drops at the same time you turn on your hose, the fertilizer may be sucked back into the drinking water pipes through the hose.  This could pose a risk to you and your family.

Common Residential Cross Connections

  • Hose bibs
  • Garden hoses
  • Boilers
  • Private wells
  • Swimming pools
  • Lawn irrigation systems
  • Residential fire protection systems
Tips for Protecting Your Household Water
keep the ends of hoses off the ground and clear of all possible contaminants.
install an approved backflow prevention device on all underground lawn irrigation systems.  Also, note that these systems require a permit.


contact your local water department if you seen any irregular or unauthorized use of a fire hydrant.
install vacumm breakers on all hose bibs in and outside your home.
close up of vacuum breaker vacuum breaker with hose bib on pipe
Vacuum breaker
Vacuum breaker installed on an outdoor hose bib
submerge hoses in buckets, swimming pools, tubs, sinks, ponds, or any standing water.
use spray attachments without a backflow prevention device.
use a hose to unplug blocked toilets or sewer pipes.

What is Backflow?

Backflow is the undesired reverse of the water flow in drinking water pipes.  This backward flow of water can occur when the following occur:

  • Back pressure:  This is when the pressure created by a boiler of other home system is higher that the water pressure inside the pipe.

  • Back siphonage:  This is when the pressure in the water pipe drops due to an unexpected occurrence like a water main break causing water to flow backward inside the water pipe.

How to Prevent Backflow

You can prevent a backflow by installing a backflow prevention device on your hose bib.  The device provides a physical barrier to backflow.  Hose bib vacuum breakers are effective backflow prevention devices, appropriate for both inside and outside hose connections.  They are available at most hardware stores, are easy to install, are low-cost.  This is a great way to protect the water in your home as well as the water in your city or town.

More Information

For additional information on cross connections, please visit the U.S. Environmental Protection Agency's website (PDF) If you have additional questions, please call MWRA's Water Quality Hotline: 617-242-5323.


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Updated May 4, 2022