Air testing is a fundamental part of the sewer adoption process, yet it’s often an area where inconsistent practices can lead to delays, failures and unnecessary remedial work.

For developers delivering assets under Section 104 agreements, demonstrating that a sewer is watertight and compliant is essential before handover to the adopting water company. Air testing provides a simple but effective method of verifying this, ensuring that new gravity sewers meet the standards set out in Sewers for Adoption and the current Design and Construction Guidance (DCG).

Why air testing matters

At its core, air testing is used to confirm the integrity of a pipeline. A watertight system prevents infiltration and exfiltration, both of which can cause long-term operational and environmental issues.

For adopting authorities, successful air test results provide confidence that installed assets meet required performance standards. For developers and contractors, getting it right first time avoids costly delays, repeat inspections and remedial works.

The basics of the test

The process itself is straightforward but must be carried out correctly to produce reliable results.

First, the section of pipeline is sealed using test bungs at either end. A U-gauge (manometer) is then connected, and air is introduced using a hand pump or bellows. The pipe is pressurised to 100mm water gauge for standard pipe testing.

Once the required pressure is reached, the system is allowed to stabilise for around three minutes. This allows temperature and pressure conditions to equalise before readings begin.

The test is then monitored over a five-minute period, recording pressure at regular intervals.

Pass and fail criteria

Clear criteria determine whether a test is successful:

  • The starting pressure for pipes should be 100mm
  • Over five minutes, the pressure must not fall below 75mm
  • This equates to a maximum allowable drop of 25mm
  • Any drop greater than this results in a fail

For gullies, lower thresholds apply, but the principle remains the same.

Importantly, not all pressure loss indicates a pipe defect. Leakage at test plugs is a common issue, so these should always be checked and secured before concluding that the pipework has failed.

Common challenges

Many failures in air testing are not due to product performance, but rather setup and execution issues. Poorly fitted bungs, incorrect pressure levels or insufficient stabilisation time can all lead to inaccurate results.

Consistency is critical. Following the correct procedure, using calibrated equipment and understanding the criteria ensures that results are reliable and repeatable.

Supporting adoption success

Air testing may be a relatively simple process, but it plays a crucial role in the broader adoption journey. It provides assurance to water companies, reduces risk for developers and supports the delivery of high-quality infrastructure.

Ultimately, successful sewer adoption depends on getting the details right, both in manufacture and installation. By embedding best practice in testing on site, contractors can significantly improve first-time pass rates and streamline the path to adoption.

Written By

Benjamin Birkhead

Benjamin Birkhead is part of the Marshalls Design Team, providing value-engineered permeable paving solutions to customers. 

Read Ben's full profile here.