Which systems need an RPZ valve?
- Joe Pettigrew
- Jun 22
- 3 min read
When managing water systems in commercial or industrial facilities, specifying the right backflow prevention is essential. A Reduced Pressure Zone (RPZ) valve plays a crucial role in safeguarding potable water against back‑pressure and back‑siphonage contamination. This guide explains which systems require an RPZ valve, referencing UK compliance standards and practical considerations for facilities managers.
What is an RPZ valve?
An RPZ valve (Reduced Pressure Zone valve) is a backflow prevention device designed to stop contaminated water from entering potable water supplies. It comprises two check valves with a pressure-monitored chamber in between and includes test cocks for annual compliance checks. In the UK, only WRAS-approved devices installed by WIAPS-accredited testers are allowed.
When is an RPZ valve needed?
Category 3 and Category 4 hazard systems
Under Water Supply (Water Fittings) Regulations 1999, risk categories determine backflow safeguards:
Category 3: slight hazard (e.g. commercial boilers, irrigation). Often use double-check valves.
Category 4 (significant hazard): requires RPZ valves. This includes systems carrying anti-freeze, chemicals, fire-sprinkler connections, or chemical dosing. RPZ valves are mandatory on these systems to prevent serious contamination.
Common applications requiring RPZ
Facilities managers should consider installing RPZ valves in systems such as:
Fire‑fighting systems with additive loops
Boiler feed lines or heat-exchanger bypasses
Chemical dosing systems
Industrial/commercial cleaning lines (descaling chemicals)
Irrigation points with pump boosters
These are typical sources of cross‑connection contamination risk where backflow protection is legally enforced.
RPZ Regulations and Compliance
Testing and accreditation
An RPZ valve must be:
Installed by a competent, accredited person (WIAPS or equivalent)
Tested annually (or more frequently if specified) using a differential pressure gauge via the valve’s test cocks
Recorded and retained for at least five years to comply with regulations
Documentation and records
Facilities teams should maintain:
Service reports and test certificates
Installation documentation with serial numbers and type approvals
Clear maintenance schedules listing all RPZ and backflow prevention assemblies
This ensures full compliance with ACOP L8, water fittings regulations, and any local water authority requirements.
Installing and Maintaining RPZ Valves
Proper installation approach
Best practice includes:
Positioning RPZ on identified hazard systems
Installing in accessible locations with safe drainage for relief valve discharge
Including bypass arrangements to allow testing without shutdown
Ensuring correct pressure drop calculations so downstream systems remain unaffected
Servicing and long-term maintenance
Keep on top of:
Annual functional testing to verify proper back-flow blockage
Checking for leaks and corrosion in the assembly
Replacing assemblies nearing end-of-life or failing test - even if intermittent discharge occurs
Aligning service intervals with other scheduled maintenance to reduce downtime
Why it matters to you
Implementing RPZ valves on Category 4 systems is not just a compliance tick-box - it significantly reduces risk of potable water contamination in your facility. It helps:
Protect building occupants and staff
Avoid enforcement actions or penalties
Meet insurers’ requirements
Uphold best practice in water safety and cross‑connection control
Internal Links
Learn more about our backflow prevention services
For full guidelines, see our RPZ valve installation guide
Wondering how this ties into Legionella control? Check our legionella remedial works page
Conclusion
Facilities with chemical dosing, boiler systems, firewater boosters or other potential hazards should equip those systems with RPZ valves. Ensure proper installation, conduct annual testing, and keep detailed records. It’s the best way to safeguard your potable water, satisfy compliance obligations, and manage risk effectively.
To find out how RPZ valves could protect your facilities or to arrange an assessment, explore our backflow prevention section at Titan Mechanical.
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