Kier wins four Thames Water AMP8 wastewater contracts worth nearly £65m

Kier has secured four contracts worth nearly £65m from Thames Water to upgrade sewage treatment works at Harpenden, Princes Risborough and Wisley, the contractor announced on 7 October under the utility's AMP8 investment programme.

The largest is a £53.7m main construction contract at Harpenden sewage treatment works in Hertfordshire, let through Thames Water's Go to Green Programme. Kier said the upgrade will increase treatment capacity by more than 50% and support growth through to 2036.

Kier was already carrying out ECI activity at Harpenden. In its August 2026 announcement of the Maple Lodge appointment, the contractor said its AMP8 support for Thames Water included early contractor involvement (ECI) activity at Harpenden.

Andy Lingham, managing director for Water at Kier Infrastructure, said: "We have worked with Thames Water since AMP6, and these latest awards are another important step in our relationship."

The four contracts

Contract	Programme	Value
Harpenden main construction	Go to Green	£53.7m
Princes Risborough	WAAP	c.£7m
Wisley initial power upgrade	Initial site-power upgrade	c.£1.7m
Wisley design services (with Binnies)	WINEP	c.£2.6m

At Harpenden, Kier said the project will modernise key parts of the works, improve wastewater treatment and help Thames Water meet tighter environmental standards while supporting the health of the River Lea.

At Princes Risborough in Buckinghamshire, a programme worth about £7m under Thames Water's Wastewater Asset Assurance Programme (WAAP) will modernise stormwater pumping, flow management, and electrical and control systems. Kier said the improvements will strengthen the resilience and reliable operation of the site.

At Wisley in Surrey, Kier is delivering an initial power upgrade worth about £1.7m, including new site-power infrastructure to support current operations and future investment. Under a separate design-services contract of about £2.6m, Kier and design partner Binnies are developing the next phase of treatment improvements, which Kier said will support the quality of treated water returned to the River Wey. That design development forms part of the Water Industry National Environment Programme (WINEP).

A Thames Water spokesperson said: "This major investment at Harpenden Sewage Treatment Works is an important step in improving river health and supporting future growth in the area."

The spokesperson added that the company will deliver the upgrades while maintaining operations at the sites and continuing to provide wastewater services to customers throughout the works. Kier said construction will be planned around the continued operation of the existing treatment works.

Phosphorus targets

Kier said the projects support Thames Water's AMP8 environmental commitments and the Environment Act 2021 target to reduce phosphorus discharged from treated wastewater by 80%.

The government's delivery plan for that target, published by the Department for Environment, Food and Rural Affairs, sets an interim goal of a 55% reduction in phosphorus loadings from treated wastewater by December 2030 against a 2020 baseline. The plan puts the value of phosphorus reduction programmes in the 2025 to 2030 water company investment cycle at £4.627bn in England.

Thames Water describes its current programme as an investment of over £20bn to fix leaks, reduce pollution and protect water quality. In September 2025 the company said additional projects would be added to its framework during AMP8, which runs from 2025 to 2030, and AMP9, from 2030 to 2035.

Kier and Thames Water

The awards follow Kier's appointment in August 2026 to the £8.7m ECI phase of Thames Water's Maple Lodge sewage treatment works upgrade. That scheme has an initial target cost of more than £265m and is described by Kier as its largest wastewater project to date.

Kier said its relationship with Thames Water has continued since AMP6. Earlier schemes include the Deephams sewage treatment works upgrade, the £66m upgrade of Mogden sewage treatment works and the £45m Faringdon to Blunsdon pipeline. The contractor also held places on Thames Water's AMP7 Capital Programmes Framework.

Kier said the Harpenden upgrade is designed to support growth in the area through to 2036.