RPZ Valve Testing

An RPZ valve (reduced pressure zone valve) is a backflow prevention device that protects the mains water supply from contamination. Under the Water Supply (Water Fittings) Regulations 1999, RPZ valves must be tested at least annually by a competent, approved tester, with results reported to the local water authority. Testing follows the RPZ Approved Installation Method (RPZ AIM), updated January 2025. 

What Is an RPZ Valve?

An RPZ valve (Reduced Pressure Zone Valve) is a backflow device which is installed onto the plumbing system to protect water from contaminants. Also known as RPZ assemblies, they are one of the safest and most reliable backflow preventer valves. However, they do require routine testing by an accredited tester approved by the Water Supply Industry.

How Do RPZ Valves Work?

RPZ valves work by maintaining a constant water pressure in the system. Within the RPZ valve body, a mechanical spring-loaded check valve opens to allow normal flow while a middle vent port sucks in atmospheric pressure. If backpressure begins siphoning water backwards, the check valve slams shut. The vent then drains out, breaking the siphon. 

This multi-barrier assembly protects the water system from potentially contaminated backflow. An RPZ valve should be installed at the point of entry of the water supply to a building or property, before any branch lines or connections. The valve should be installed on the cold water supply line and downstream of any backflow preventer or check valve.

Why RPZ valves must be tested

RPZ valves are required by law to protect the mains water supply from backflow contamination. Over time the internal check valves and relief valves can degrade, clog, or fail, and the only way to confirm they still work is a formal pressure test carried out by an approved tester using calibrated equipment.

Under the Water Supply (Water Fittings) Regulations 1999, RPZ valves must be tested at intervals set by the local water authority, at least annually and sometimes more frequently. Testing follows the RPZ Approved Installation Method (RPZ AIM), most recently updated in January 2025, and must be carried out by a tester registered with an approved contractor scheme such as WIAPS (the Water Industry Approved Plumbers Scheme).

After each test, the report must be submitted to your water authority within 10 working days. If a valve is not tested as required, your water authority can issue an enforcement notice under the Water Industry Act 1991, attend your premises to carry out the test themselves, and recover their costs from you. We handle the testing, the certification, and the water authority submission on your behalf, so nothing falls through the gap.

How Often Do RPZ Valves Need to Be Tested?

At least every twelve months, as set by your local water authority. Some authorities may require more frequent testing depending on the risk profile of the installation. The interval is a condition of the water authority’s consent to have the valve installed in the first place, so missing a test is not just a compliance gap, it puts your consent at risk.

There is a good reason why water regulations are so stringent. Backflow can cause all sorts of problems with water hygiene, from introducing contaminants into the water system to causing flooding. RPZ valves are a crucial part of preventing backflow, so they must be well-maintained and regularly tested.

What Does RPZ Valve Testing Involve?

RPZ valve testing involves checking the water pressure, check valves, and relief valves to ensure they are functioning correctly. An accredited RPZ valve tester will also check for any leaks in the system which could cause contamination.

Once testing is complete, We will issue you with an RPZ test report to prove that you have complied and that your RPZ valves were functioning properly at the time of the test.