New York State Sanitary Code 5-1.31 requires the complete containment of water on many commercial customers’ property by use of an approved backflow prevention device i.e. RPZ, DCV, or air gap. Under state regulations governing the requirements for backflow prevention devices, the Suffolk County Department of Health requires controls be in place for hazardous operations under private control in order to safeguard the water supply. Further information can be obtained by contacting the Suffolk County Department of Health directly or our Cross Connection Control Department. Both are listed on the last page of this document.


The "RPZ/DCV" device, as it is commonly referred to, is a backflow prevention device used to prevent "backflow" of foreign liquids and other matter into the potable supply of water which could result in contamination. Backflow can occur when the pressure in our system is less than the pressure in a customer’s system. For example if a fire department were to draw too much water while fighting a fire, it would reduce the pressure in the area’s water main below that which exists in, say an industrial building, thus back-siphoning chemical mixtures from the building into the water main through cross connections. This could contaminate the area’s water. While uncommon, pressure differentials can happen and protective devices must be used as required by law to protect the water supply.
The RPZ/DCV device which actually prevents the backflow of water stays open when water is flowing in one direction only. If a change of direction occurs, as it would during a major reduction in pressure, the RPZ/DCV device would close and prevent a contamination backflow.


Domestic Water Service Requirements

Newly constructed Commercial Buildings are required to install a Reduced Pressure Zone (RPZ) device.
Existing commercial buildings will require the installation of either a Reduced Pressure Zone Assembly (RPZ) or Double Check Valve (DCV), based upon degree of hazard determined by the Cross Connection Department under NYS Department of Health guidelines and Suffolk County Water Authority Rules & Regulations. 
While residential backflow prevention is not mandated by law, residential accounts with high degree of hazard are required by SCWA to install a RPZ device. These include, but are not limited to, private well(s) connected to the house, chemical-fed irrigation systems, and geothermal HV/AC systems. All of the above require an approved backflow preventer commensurate with the degree of hazard, which is determined by the Cross Connection Department at SCWA.
New non-residential dock services also require an RPZ device.

Fire-Flow Requirements and Effects

RPZ/DCV devices while very effective in protecting the water supply from backflows can cause reductions in pressure and fire-flow capacity. Fire-flow capacity is regulated by fire departments, fire marshals, fire underwriting agencies and other regulating agencies.  While we realize the importance of maintaining good fire protection, the installation of an approved backflow prevention device is essential in protecting the water supply. Contact the Cross Connection Department for options for fire line backflow device installations.
New construction buildings, services over 2" on existing buildings, and fire lines services require plans be filed. Please refer to our Cross Connection Booklet which will aid you in the filing procedure.