What is backflow?

Most buildings in New York City are connected to the city water supply system, which is normally pressurized up to about 40 psi. Even if your building does not have a pump, the water coming into the building from the city is under enough pressure to allow it to flow freely from the street into the building's water piping network. Most of the time the water flow goes in one direction: into the building. There are situations, however, where something that is connected inside the building pipe network (say, a roof tank) will create back pressure causing the water to flow the other way: back into the street. If this water contains any kind of toxins or chemicals, it can contaminate the city water supply. For this reason, backflow prevention is essential.

How does backflow prevention work?

There are two main types of backlow preventers: a double check valve (DCV) and a reduced pressure zone (RPZ).

The DCV is simply an assembly of two check valves piped in a series. This assembly is installed in the water line coming into the building. The check valves allow water to flow only into the building. If for some reason there is backflow in the building pipe network, the water will stop at the backflow preventer check valve before it gets into the city's main water supply. If the first check valve fails, the second check valve in place as backup.

The RPZ device operates similarly to a double check valve. The main difference is that when there is a change in pressure and the water flows in the wrong direction, the water is bypassed and drained out of the system. This provides an extra layer of protection. RPZ devices are typically required in more hazardous applications.

When is a backflow preventer needed?

 The DEP has many regulations. The simple guide below can help you determine if your building is at risk for backflow and what kind of preventer (DCV or RPZ) would best support the building. The chart covers common facilities found in New York City.

Received a violation notice?

There are a few simple procedures to alleviate a DEP violation and install the proper backflow device in your facility:

1. Contact an engineer to prepare a letter to the DEP stating that the engineer will be addressing the violation. This must be done within 30 days of receiving the violation notice.
2. Engineer will prepare the backflow preventer plans per DEP requirements.
3. Plans must be submitted with a GEN236 form, prepared by the Engineer. The building wwner must sign the form.
4. Once the DEP approves the plans, the building owner must retain a licensed backflow installer (plumber) to perform the work as prescribed in the plans.
5. The plumber will be responsible for pulling a permit with the NYC DOB.
6. Once the installation is complete, a licensed backflow testing company (can also be the plumber) will test the device, and prepare a GEN215B form stating that the device passed the test.
7. The engineer will inspect the installation and sign off on the GEN215B form.
8. The DEP also requires a DOB inspection for the plumbing work that was performed.

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