Backflow Prevention Requirements in New Hampshire
Backflow prevention is a regulated component of potable water system integrity in New Hampshire, governing how licensed plumbers, property owners, and water utilities protect drinking water supplies from contamination caused by pressure reversals. The requirements apply to residential, commercial, and industrial connections and are enforced through a combination of state plumbing code, local ordinance, and water purveyor rules. Compliance involves device selection, installation by qualified personnel, and periodic testing by certified testers.
Definition and scope
Backflow is the unintended reversal of water flow within a distribution system, which can draw contaminants — chemicals, biological agents, or non-potable water — into a potable supply. Two physical mechanisms produce backflow: backsiphonage, caused by negative pressure in the supply line (such as during a water main break or high-demand event), and backpressure, caused by downstream pressure exceeding supply pressure (common in boiler systems and elevated storage).
New Hampshire's backflow prevention requirements are grounded in the New Hampshire Plumbing Code, which adopts the International Plumbing Code (IPC) with state-specific amendments (New Hampshire Plumbing Code Amendments). The applicable administrative authority at the state level is the New Hampshire Office of Professional Licensure and Certification (OPLC), which oversees plumbing licensure. Local water utilities and municipalities may impose additional cross-connection control programs beyond the minimum state code requirements.
Scope and coverage: This page addresses backflow prevention as it applies to plumbing systems within the State of New Hampshire. Federal Safe Drinking Water Act (SDWA) requirements administered by the U.S. Environmental Protection Agency (EPA) establish baseline protections but are implemented and enforced at the state level through the New Hampshire Department of Environmental Services (NHDES). Municipal water system cross-connection programs, private well systems, and systems governed solely by federal facility rules are adjacent topics; private well intersection points are addressed separately under New Hampshire Private Well Plumbing Requirements. Interstate water utility issues are not covered here.
How it works
Backflow prevention devices create a physical or mechanical barrier that allows forward flow but blocks reverse flow. Device selection is determined by the degree of hazard presented by the downstream use — a classification framework defined under the IPC and the American Society of Sanitary Engineering (ASSE) product standards.
The primary device categories and their application boundaries are:
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Air Gap (AG) — The only non-mechanical method; requires a physical separation of at least twice the diameter of the supply pipe (minimum 1 inch) between the outlet and the flood level rim of the receiving vessel. Suitable for high-hazard applications. No moving parts; not subject to mechanical failure.
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Reduced Pressure Zone Assembly (RPZ / RPZA) — Required for high-hazard connections such as boiler chemical feed systems, irrigation systems with chemical injection, and industrial process lines. Provides the highest mechanical protection; consists of two independently acting check valves separated by a reduced pressure zone with a differential pressure relief valve. Must be tested annually by a certified tester (ASSE 1013).
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Double Check Valve Assembly (DCVA) — Appropriate for low-hazard connections such as fire suppression systems without chemical additives and commercial irrigation without fertilizer injection. Consists of two independently acting check valves. Also requires annual testing.
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Pressure Vacuum Breaker (PVB) — Protects against backsiphonage only; commonly used on residential irrigation systems. Must be installed at least 12 inches above the highest downstream outlet. Cannot be used on systems subject to backpressure.
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Atmospheric Vacuum Breaker (AVB) — Single-use, non-testable; acceptable only where no downstream shutoff valves are installed. Limited to low-hazard, non-continuous-pressure applications.
The full regulatory and operational framework is detailed on the regulatory context for New Hampshire plumbing reference page.
Common scenarios
Backflow prevention applies across a range of installation contexts in New Hampshire:
- Residential irrigation systems: A PVB or DCVA is required at the point of connection to the potable supply. Systems incorporating fertilizer or pesticide injection require an RPZ. See New Hampshire Irrigation System Plumbing for additional installation depth requirements.
- Commercial food service: High-hazard classification applies to any connection where food-grade or chemical substances can enter supply lines; RPZ or air gap is required.
- Water heaters and boilers: Thermal expansion and chemical treatment circuits create backpressure conditions. RPZ assemblies are standard for boiler chemical feed lines. New Hampshire Water Heater Regulations addresses thermal expansion device requirements that interact with backflow protection.
- Fire suppression systems: DCVA is the baseline requirement for systems without antifreeze or chemical additives; RPZ is required if additives are present.
- Water softeners and treatment equipment: Ion exchange and chemical dosing systems connected to potable lines require cross-connection control devices; see New Hampshire Water Softener Plumbing.
- Seasonal and vacation properties: Winterization procedures that involve draining or pressurizing systems with non-potable sources require verified backflow protection upon recommissioning. New Hampshire Vacation Home Plumbing covers seasonal disconnection and restoration protocols.
Decision boundaries
The determination of which device is required depends on three classification factors: hazard degree (high vs. low), pressure condition (backsiphonage only vs. backpressure-capable), and continuity of pressure (continuous vs. intermittent).
| Factor | High Hazard | Low Hazard |
|---|---|---|
| Backpressure possible | RPZ or Air Gap | DCVA |
| Backsiphonage only | RPZ or PVB | PVB or AVB |
Installation must be performed by a licensed plumber holding a valid New Hampshire license; backflow device testing must be performed by a tester certified under a program recognized by NHDES or the applicable water utility. The New Hampshire Master Plumber License and New Hampshire Journeyman Plumber License credential categories define the scope of installation authority.
Permits are required for new backflow prevention device installations and for replacement of testable assemblies in most jurisdictions. Inspection and test records must be maintained and submitted to the water purveyor on the schedule established by the local cross-connection control program — typically annually for RPZ and DCVA assemblies. Additional permitting and inspection concepts are outlined at the New Hampshire plumbing authority index.
Properties with lead service line remediation work underway have parallel considerations; New Hampshire Lead Pipe Remediation addresses interaction between cross-connection control and lead service replacement projects. New Hampshire Drinking Water Plumbing Standards covers the broader potable water quality framework within which backflow prevention operates.
References
- New Hampshire Office of Professional Licensure and Certification (OPLC)
- New Hampshire Department of Environmental Services (NHDES) — Drinking Water and Groundwater Bureau
- U.S. Environmental Protection Agency — Safe Drinking Water Act
- International Plumbing Code (IPC) — International Code Council
- ASSE International — Product Standards (ASSE 1013, ASSE 1015, ASSE 1020)
- New Hampshire Revised Statutes Annotated (RSA) Title XXX, Chapter 329-A — Plumbers