Mains Replacement Programme for Dŵr Cymru Welsh Water

Mains replacement programme for Dŵr Cymru Welsh Water

Case study

In response to a specific performance commitment deliverable (PCD), Dŵr Cymru Welsh Water tasked us with developing an optimal asbestos cement mains replacement programme. The goal was to deliver maximum value for customers, address all relevant PCDs, and keep rehabilitation costs below an average of £292 per metre.

Asbestos cement mains make up around 12% of Dŵr Cymru Welsh Water's network by length, yet they account for approximately 40% of all mains repairs, a figure expected to rise significantly in the coming years.

We delivered the first batch of asbestos cement mains schemes – covering approximately 950km of mains – in just three months. This success led to a full company-wide rollout. We developed schemes covering multiple times the required length and budget for AMP8, giving Dŵr Cymru Welsh Water the flexibility to select the most cost-effective and beneficial portfolio of projects.

After completion of the company wide asbestos cement mains replacement programme project, we were challenged by Dŵr Cymru Welsh Water’s managing director to identify and develop schemes for the remaining worst-performing assets in the business.

Framing the challenge

Dŵr Cymru Welsh Water needed to identify the most effective mains replacement schemes that would:

Meet the PCD challenge of keeping average rehabilitation costs below £292/m
Deliver the best value to customers
Improve performance across all key outcome delivery incentives (particularly water quality and customer acceptability)
Align with Ofwat’s expectations for accelerated and optimised delivery
Be fully auditable and transparent in relation to the benefits to customers

The key issue was how to quickly and accurately identify which assets to prioritise.

Traditionally, targeting and prioritisation of the assets to focus on were done at a zonal level, which risked overlooking poorly performing assets within otherwise well-performing zones.

To overcome this, we developed a new approach that bypasses zonal-level assessments and directly identifies the worst performing mains assets across the entire network. This was a game-changing shift in methodology.

Our process identified the small percentage of assets that were responsible for the majority of performance-related issues and risks throughout Dŵr Cymru Welsh Water. The insights were transformative.

Approach and implementation

Our approach included the following steps:

1. Company-wide assessment of worst-performing mains assets

Identified, ranked on cost vs benefit, then prioritised the worst-performing mains assets across the entire network.

2. Scheme optimisation

Carried out at a zonal level so that all assets could be assessed holistically. Worst-performing mains assets are validated and optimised into a deliverable scheme, combining assets where appropriate.

3. Cost-benefit analysis

Delivered full cost-benefit analysis for each scheme, including accurate implementation costs and '£ spent' vs '£ benefit' return-on-investment values.

4. Deliverables

Zonal dashboards, scheme templates, interactive geospatial plots, and transparent and auditable evidence base.

We developed schemes covering 5+ times the required AMP8 mains length/budget, enabling Dŵr Cymru Welsh Water to draw upon a centralised portfolio of schemes to select the most beneficial projects while maintaining an average replacement cost below £292/m.

This approach was applied without bias toward region, material type, or pipe diameter – ensuring a truly data-driven, company-wide prioritisation.

Impact and outcomes

Over 7,500 worst-performing mains assets identified, covering:
- >99% of all mains repairs
- 30% of interruption to supply issues
- 10% of leakage
- 20% of low-pressure complaints
- 70% of event-driven water quality issues
- 60% of worst-served customers
Worst-performing mains assets made up only 4.5% of total asset stock by length
13 primary data sets used, including GIS, AddressPoint, OS MasterMap, CML (ITS), condition and deterioration models, leakage, repairs, complaints, water quality samples, worst-served customers, network models, and cost estimation - unit cost data models
5.4 million records processed, averaging 33 fields per record to total over 179 million data points
12,000+ lines of code adapted for bespoke analyses
100+ sequenced tasks to transform raw data into fully evidenced, cost-benefit analysed scheme outputs
All schemes and outputs are manually validated by a team of highly experienced water infrastructure design engineers
No black box: All work done in off-the-shelf software and fully transparent and auditable

All outputs were delivered in Power BI dashboards and Python HTML, including full zonal outcome delivery incentive assessments and detailed scheme templates.

We delivered mains replacement schemes covering more than 2,300 km with an estimated combined cost value of £1.02 billion and an estimated combined benefit value of £15.9 billion. Our fee equates to less than 0.001% of the value of the schemes we delivered.

For clients who may have already scoped out mains replacement schemes for the early years of the AMP8, our process can determine how beneficial their investment may be across all outcome delivery incentives.