Cross Connection Control

The City of Cambridge Water Department spends millions of dollars each year to insure the safety of our drinking water. A vital link in this effort is the Water Department's Cross-Connection Control and Backflow Prevention Programs.

Water distribution systems are designed so that water flows in one direction from the treatment plant to the customer. Cross connections are any unprotected actual or potential connection or structural arrangement between a public or a consumer's potable water system and any other source or system through which it is possible to introduce into any part of the potable system any used water or substance other than the intended potable water. Bypass arrangements, jumper connections or any other temporary or permanent connections through which backflow can occur are considered to be cross connections.

Backflow is the undesirable reversal of flow of water or mixtures of water and other liquids or substances into the distribution pipes of the potable supply of water from any source or sources.

Federal and State laws require Water Purveyors to protect their system from cross connections and backflow. To do this, we work closely with consumers, architects, engineers and contractors to ensure that all those who are required to comply with cross connection control and/or backflow prevention requirements will do so.

For more information about this program, please contact the Water Department at 617-349-4770 or by email at

Backflow Prevention

Preventing backflow is an important part of maintaining a healthy water supply. The City of Cambridge's water distribution system is designed to carry water from the water treatment plant to the consumer. Cross connections, or connections between potable water in the distribution system to any non-potable water, exist. These connections make the water distribution system susceptible to backflow, which is the reversal of water flow from its intended direction. In other words, non-potable water could be introduced into the distribution system.

There are two types of backflow:

Three Common Types of Backflow Prevention Devices for Irrigation Systems

Pressure Vacuum Breaker.
This device is approved for irrigation systems, however it is rarely used because of above ground installation and is subject to freezing during winter months. This device is also approved for chemical injection systems on sprinklers. Irrigation system can be turned off at 1 of 2 shut off handles.

Atmospheric Vacuum Breaker.
This device is commonly found on older sprinkler systems, but is not approved for new installations because it is non-testable. It must be replaced by a Double Check Valve when upgrading irrigation system. No shut off handles to isolate irrigation system.

Double Check Valve.
This is the most widely used backflow prevention device on sprinkler systems. It is installed below grade in a standard valve box. Irrigation system can be turned off at 1 of 2 shut off handles.

Simple Steps to Prevent Backflow:


Permit hours for the Cross Connection Program and Hydrant Rental are: Monday thru Friday 7:00am-3:00pm at the Cambridge Water Department 250 Fresh Pond Parkway, Cambridge, MA