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Backflow Prevention: It’s the Law

Our 14-story, 90-unit cooperative on the Upper East Side recently had a condition assessment performed by an engineer to help with future capital planning. They informed us that we need to install backflow preventer devices on our building’s water service lines because it is mandated by the city. I’ve lived in this building for 30 years and have been on the board for 10 years. Why exactly do we need backflow preventers, and why is this the first I’ve heard about this requirement?

One billion gallons of drinking water are distributed to the taps of nearly nine million New Yorkers each day, and it’s vital to keep this water clean. The water supply system, overseen by the New York City Department of Environmental Protection (DEP), includes roughly 6,800 miles of water pipes below our city’s streets. The water is clean and potable, but there’s a potential for contaminated water to flow back into the city’s water supply via back-pressure or back-siphonage. The solution: properly installed backflow prevention devices.

Since 1980, backflow preventers have been legally mandated for certain buildings by the New York sanitary code and the rules of the city of New York. The regulation was not strictly enforced until a push in recent years by the DEP’s cross-connection control program, an initiative that includes random inspections of buildings, including residential dwellings with large or treated boilers, roof tanks, cooling towers, and multiple water service lines.

What Is Backflow?

Backflow is the reverse flow of non-potable water – such as chemically treated water from boilers – back into the public system. Contamination can occur at any point of connection between a potable-water pipe and a source or system containing non-potable water and other unwanted materials, also known as a cross connection. Back-pressure backflow results when the pressure in the system is greater than the pressure of the incoming potable water. Backpressure can be caused by pumps or temperature increases in boilers, or if there is a decrease in the water-supply pressure. Back-siphonage occurs when negative or reduced pressure develops in the supply piping and forms a vacuum, usually because of an interruption or drain in the supply, such as water-main repairs or breaks. To prevent backflow, a device is installed on each main water service line – domestic and firefighting water – feeding the building.


Installation requires the services of a licensed professional engineer or a registered architect and also a licensed master plumber. These professionals can help you determine if your building requires a backflow preventer or multiple devices, or if you qualify for an exemption. Exemptions must be filed with the DEP by an engineer or architect. If your building has an existing backflow preventer but the DEP has no record of its installation, you must have a licensed professional file a record drawing and an initial test report of the device to the DEP.

Responsibility for installation falls upon the owner of the property or the co-op or condo board. Owners and boards of buildings that are issued an order by the DEP to install a backflow preventer must file plans with the DEP within 30 days. If the DEP has not received certification that the device is in the process of being installed within that time, the Environmental Control Board (ECB) will issue a violation, which could result in a civil penalty of up to $1,000. Continued non-compliance can ultimately lead to civil and criminal actions, as well as termination of water service.
It can take several weeks to install a backflow preventer. First, plans for each device must be drawn up by an architect or engineer, and an application for approval sent to the DEP. That may take up to three weeks or more to process. Rejected plans must be revised and resubmitted, which can add another several weeks.

Approved plans are then filed with the New York City Department of Buildings (DOB) and a plumbing permit is issued. Installation typically takes just a few days. Proper planning is needed to minimize disruption to residents and any businesses located in the building. An engineer or architect must inspect each device after installation, and a state-certified backflow prevention device tester needs to evaluate the system as well. Within 30 days, a test report must be submitted to the DEP.


Costs vary based on the specific site conditions, the size and quantity of the water service(s), and the proximity to a floor drain. Prices range from a base of $7,500 to $15,000 for midsize buildings and $15,000 to $35,000 for larger ones; this does not include the engineer’s or architect’s fees. The DEP filing fee is $350 per service connection and the DOB filing fee is a little over 1 percent of the estimated plumbing cost. The size of the device is also a factor. For example, a one-inch device can start at $225, while a three-inch device could cost $2,800. Labor also increases with pipe size. Because these devices are made up of moving parts, seals, and springs that are subject to corrosive substances, wear, and fatigue, it’s critical to maintain them to ensure they operate properly and play their part in keeping drinking water safe.

The addition of a backflow preventer reduces water pressure to the building; additional, more significant costs can occur if the drop in water pressure becomes an issue. An engineer or architect can help determine if installing a pump or larger-size water service and backflow prevention device would counteract this loss.

Finally, the law requires an annual inspection by a certified tester and a report to the DEP. Failure to comply can lead to penalties and termination of water service. 

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