Restormel WTW (2025)

Restormel WTW - Courtesy of Galliford Try
As part of South West Water’s ongoing commitment to delivering safe, clean, and high-quality drinking water, significant investment has been made to upgrade and future-proof the Restormel Water Treatment Works (WTW). The site, originally commissioned in the 1960s, has been incrementally expanded over several decades and now plays a pivotal role in maintaining potable water supply resilience to a large proportion of the Cornwall population. Given the increasing demand on water infrastructure, both from a growing residential population and the seasonal impact of tourism, projects such as this form a vital component of South West Water’s wider strategic planning for AMP7 and beyond.
Purpose of the project
The primary objective of this capital scheme was to reduce the levels of total manganese in final treated water at the Restormel WTW, in order to help mitigate the risk of discolouration events in customer supply. Although the existing treatment facility manages a broad range of water quality risks effectively, manganese remained a persistent challenge due to diffuse sources in the catchment area.
This upgrade project specifically focuses on integrating pressure filters downstream of the chlorine contact tank, enabling final manganese concentrations to meet more stringent internal quality standards.

Restormel WTW – Courtesy of Galliford Try
Background: Challenges & drivers
South West Water regularly reviews source water quality risks through comprehensive catchment studies and industry-recognised methodologies. The raw water treated at Restormel is drawn from a catchment considered to be rural in nature, and as such, it is subject to a range of microbiological and chemical risks, including biological waste, colouration, herbicide residues, and low-level, widespread manganese.
The Water Quality (WQ) team determined that while current treatment processes adequately control most parameters, manganese posed a risk to compliance and customer experience. While not a health risk, manganese can accumulate in distribution and contribute to customer complaints regarding discolouration. Consequently, this scheme was prioritised under South West Water’s Quality Enhancement (Q) programme.
Process integration & technical approach
The upgraded process introduces a new treatment stage specifically designed to target and remove manganese. The scheme design routes partially treated water through an interstage pumping station into a new manganese plant, where pressure filters remove residual manganese.
The new equipment was carefully integrated into the existing site layout, ensuring the plant could be operated with minimal disruption to live operations. This approach supported a smooth transition to the new process stream and minimised downtime during commissioning.
The key infrastructure elements included:
- Process diversions and interstage pumping systems.
- Pressure filter vessels and associated pipework.
- New MCCs and electrical systems.
- Service upgrades including HV diversions and power supply amendments.
- New process control and telemetry infrastructure for operational integration.

Restormel WTW – Courtesy of Galliford Try
Delivery strategy & timeline
Galliford Try were engaged as the Principal Contractor, responsible for all phases of the project from outline design through to commissioning and handover.
The delivery strategy focused on collaborative working, digital design integration, and progressive risk management.
Restormel WTW: Supply chain – key participants
- Main designer/contractor: Galliford Try
- Civils design: Eastwood Consulting Engineers
- Ground investigation: AGS Ground Solutions Ltd
- Piling contractor: Aarsleff Ground Engineering Ltd
- Piling: Saxton Drilling Ltd
- RC contractor: D Wall Construction Services Ltd
- Diamond drilling: Ace of Diamonds Ltd
- Electrical installation: Drew & Co (Electrical Contractors) Ltd
- HV designers: ITP Electrical
- HV installation: Nick Piper Ltd
- HV transformer: Wilson Power Solutions Ltd
- Structural steel: Minear Engineering Ltd
- Precast manholes & chambers: Frazer Civils Infrastructure
- Portal frame building: Hewaswater Engineering Ltd
- Underpressure connections: UTS Engineering Ltd
- Process pipework: JBF Group
- Ductile iron pipework: Electrosteel Castings (UK) Ltd
- Trace heating & lagging: Jade Insulation Ltd
- Contact filters: LTi Vessco
- Blowers: AERZEN Machines Ltd
- Pumps: Bedford Pumps Ltd
- Static mixers: Statiflo International Ltd
- Clean washwater: Alpha Plus Ltd
- Valves: Affco Flow Control (UK) Ltd
- Actuators: Rotork Controls
- Flow meters & instrumentation: Siemens
- Filter media: Western Carbons Ltd
- Kiosks: Quinshield Ltd
- Tree surgery & planting: Glendale Services
- Security doors & covers: Technocover Ltd
- Security fencing: Topan Group
Outline design phase
Initial concept work included high-level optioneering, site surveys, planning applications, and development of key deliverables such as PFDs, process calculations, and mass balances. These outputs informed robust cost forecasting and risk management plans.
Detail design phase
During this phase, Galliford Try led the coordination of multi-disciplinary design inputs (civil, mechanical, electrical, and ICA) bringing together supply chain partners for early engagement. Hazard studies, constructability reviews, buildability assessments, and stakeholder walkthroughs ensured alignment with operational expectations and site constraints.
Construction design & implementation
A fully federated 3D model was developed using Revit and Navisworks, enabling detailed clash detection, layout optimisation, and design coordination across all trades. The integration of subcontractor designs was closely managed to ensure all elements were construction-ready and compliant with Regulation 31 standards for materials in contact with potable water.

Restormel WTW – Courtesy of Galliford Try
Construction & commissioning
Construction works included earthworks, reinforced concrete foundations, pipeline installations, ducting, drainage and specialist installations for the interstage pumping station and pressure filters. Multiple subcontractors were engaged to deliver specialist packages such as piling, structural steelwork, HV installation, and mechanical assembly. Galliford Try’s own commissioning engineers delivered the electrical, ICA, and process commissioning scopes.
Electrical infrastructure & power strategy
As a result of increased electrical loading, modifications to the existing electrical infrastructure were required. A revised connection agreement was secured with the local distribution network operator (DNO), and the design team undertook load flow analysis and protection studies to support the safe integration of the new equipment. New transformer and switchgear infrastructure were installed to streamline installation and reduce the extent of civil works. This approach helped minimise operational risk while supporting a more maintainable and efficient plant layout.
All installation, testing, and commissioning activities were overseen by a dedicated Senior Authorised Person (SAP) from Galliford Try, ensuring compliance with relevant electrical safety standards and protocols.
Temporary works & site management
Galliford Try’s in-house temporary works department managed the design and installation of all temporary supports, including cofferdams for excavations, piling platforms, crane bases, and scaffold structures. Designs were subject to CAT II checks where required and reviewed in partnership with subcontractors for high-risk elements such as working at height and excavation near existing assets.
Innovation & value engineering
Several opportunities for efficiency and value improvement were identified during the design stages:
- Dirty washwater reuse: Rather than installing a new dedicated washwater system for the manganese plant, existing capacity within on-site infrastructure was utilised. This solution reduced both the construction programme and overall cost.
- MCC optimisation: The enhanced design deployed remote instrumentation and control panels at strategic points, rather than housing all equipment in a centralised motor control centre (MCC). This reduced cable runs, equipment footprint, and improved long-term maintainability.
- Access redesign: The interstage pumping station access was reconfigured to eliminate the need for overhead structures. This improved drainage, minimised water ingress risk, and reduced noise levels associated with pump operations.
- Relocation of HV equipment: This reduced infrastructure cost and facilitated safer construction sequencing.

Restormel WTW – Courtesy of Galliford Try
Environmental & carbon performance
Sustainability was at the heart of the scheme from the outset. Galliford Try utilised the MOATA Carbon Calculator across the Outline and Construction Issue design stages to evaluate embedded carbon in key assets and process areas. The federated 3D model provided accurate volumetric and materials data, which allowed the project team to identify areas for improvement; such as reduction in concrete usage, steel reuse, and process optimisation for energy efficiency. Carbon performance was monitored as a project KPI and contributed positively to South West Water’s AMP7 environmental commitments.
Health, safety & site culture
The project operated under the Galliford Try Business Management System and was subject to frequent audits by South West Water’s Health, Safety and Environmental teams. The scheme achieved a Gold Site Pride Award following an audit in late 2024, with the award formally presented in January 2025. Key to this success was the proactive engagement of the delivery team in planning, toolbox talks and regular behavioural safety observations.
Stakeholder engagement & training
Throughout the project, close collaboration was maintained with South West Water’s operations, water quality, and capital delivery teams. As part of the handover, comprehensive training was delivered to site operatives, and draft O&M manuals were issued at the COU (Confirmation of Use) stage. Final documentation and H&S files followed at the OA1 (Operational Acceptance) milestone.
Conclusion
The Restormel WTW upgrade represents a model of collaborative delivery, technical innovation, and sustainability in action. The successful integration of a new manganese removal process within an operationally critical and complex live site, demonstrates South West Water and Galliford Try’s shared commitment to delivering better outcomes for customers and the environment.