Testwood Water Treatment Works – Southampton

Non-destructive testing and structural investigations to the rapid gravity filters at Testwood Water Treatment Works

The challenge

Owned by Southern Water, Testwood Water Treatment Works is the largest in Hampshire. The Works draw 136 million litres of water a day from the River Test which are treated before supplying residents in Totton, Waterside, Southampton and the Isle of Wight. Testwood also supplies the Esso oil refinery at Fawley.

Non - Destructive Testing

Southern Water identified that repairs needed to be made to Testwood’s rapid gravity filters to make sure they could maintain the safety and quality of the water supply. These works were part of a wider project to reduce contamination risks, which should be completed in 2025.

Inertia Consulting Ltd were appointed to carry out a series of non-destructive tests and investigations to provide the data needed for the Contractor, Stonbury, to design a repair scheme for the rapid gravity filters and associated facilities.


“Very good, efficient, helpful and very in depth services offered and to a very high quality and standard.”

Paul Dart, Contracts Manager, Stonbury

The works spanned the full suite of non-destructive testing methods to the filters themselves and the structural elements within the filter building. This included a full hammer visual survey. Our engineers then produced a detailed report including drawings that indicated the precise location and nature of the required repairs.

Our inspection and testing works required confined space and difficult access working to access the filters and surrounding structures. The project therefore required comprehensive risk assessments for each stage of the works. The works were planned to ensure minimum disruption to the water supply to homes and businesses.

The outcome

The project was completed successfully, helping to ensure that residents supplied by the Testwood Water Treatment Works can continue to enjoy a supply of safe, uncontaminated drinking water for years to come.

The project team
  • Southern Water plc – the Client
  • Stonbury – Contractor
  • Inertia Consulting Ltd – Survey and Inspection Consultant