West Berkshire Groundwater Scheme

Information statement — 26 August 2026

In summary: The West Berkshire Groundwater Scheme pumps water from the deep aquifers in the Kennet, Lambourn and Pang catchments, in to those rivers, to supply the reservoirs of west London during extreme drought. ARK recognises the West Berkshire Groundwater Scheme as an emergency resource that can help maintain public water supplies during a genuinely severe drought. We do not accept it as a routine source of water supply. Operation must be accompanied by transparent monitoring, clear limits and evidence about effects on groundwater recovery and future chalk-stream flows.

Background

The West Berkshire Groundwater Scheme was developed in the 1970s and is owned and operated by the Environment Agency. It comprises 32 boreholes, pumping stations and a network of pipelines and outfalls. In drought, groundwater is abstracted from the Chalk and Upper Greensand aquifers and discharged into watercourses including the Rivers Pang, Lambourn, Kennet, Enborne and Loddon, the Winterbourne Stream and Foudry Brook.

The added flow travels downstream towards the River Thames, enabling abstraction for public water supply when reservoir storage and river flows are under severe pressure. The scheme is licensed for drought, drought-recovery and low-flow purposes and is intended to be used infrequently.

The scheme can have an immediate local benefit by increasing river flow during drought. However, that water is drawn from the same groundwater system that sustains chalk streams. Its longer-term effect depends on the volume and duration of pumping and on subsequent winter recharge. The scheme has only been used a handful of times since its creation.

In 2020, Jacobs completed an Environmental Impact Assessment of the scheme for the Environment Agency. It assessed the likely effects of discharging water into the receiving rivers, including changes in flow, water quality and temperature, erosion and channel form, ecology, and risks to people and communities. They concluded that the scheme could operate for drought support without significant environmental effects, provided mitigation, monitoring and operational controls were applied. Potential local risks included erosion or scour at some sites, temporary ecological effects and rapid increases in river level and velocity that could affect public safety. The study focused on impacts in the receiving watercourses; it did not assess the effects of abstraction on groundwater storage or predict aquifer recharge and recovery times after operation.

Latest update

July 2026 was the driest July in the Thames area since records began in 1871: only 1mm fell, around 1% of the long-term average. Across April to July, the Thames area received just under half its expected rainfall, making it the fourth-driest such period on record. The combination of prolonged warmth, very dry soils and exceptionally low July rainfall drove river flows and reservoir storage down.

The Thames area entered drought status on 29 July 2026. The Environment Agency subsequently notified ARK that Thames Water had requested operation of the scheme because water levels in its West London reservoirs were low and falling. Phased pumping was scheduled to begin from 24 August 2026.

The latest information available to ARK confirms the request and planned start for the Pang, Enborne and Loddon wellfields. There are no current plans to use Lambourn, Shefford or Winterbourne and there are no details on operating duration, total abstraction volume or an assessment of how quickly groundwater levels are expected to recover.

ARK’s position

ARK recognises the West Berkshire Groundwater Scheme as a strategic resource for genuinely extreme droughts only. We do not support its use as a routine substitute for resilient water-resource planning, leakage reduction or sustained demand management.

In the present circumstances, we recognise the need to maintain essential public water supplies. Any apparent benefit of more water in a river channel must not obscure the fact that the water has been removed from aquifer storage. If winter recharge is poor, operation could reduce groundwater levels available to support river flows in the following season.

ARK has asked the Environment Agency for evidence from previous operations and for modelling or monitoring that explains the expected scale and timing of groundwater recovery. We have not yet received a substantive answer to that question. Until this evidence is available, the longer-term effects are unknown.

What ARK expects during operation

• Proportionate operation: pumping should be limited to the minimum volume and duration needed for the drought response.
• Transparent reporting: the Environment Agency and Thames Water should publish operating dates, volumes, affected reaches and the criteria for reducing or stopping pumping.
• Environmental monitoring: groundwater levels, river flows, water quality, temperature, erosion, ecology and public-safety risks should be monitored before, during and after operation.
• Recovery assessment: monitoring should continue through the recharge season and findings should be made publicly available.
• Demand management: emergency operation should sit alongside visible action on leakage, water efficiency and restrictions on non-essential demand.

Safety and reporting concerns

Scheme activation can cause relatively rapid increases in river level and velocity downstream of outfalls. People should take extra care near the water’s edge. Pollution, unusual odours, erosion, fish in distress or other environmental incidents should be reported to the Environment Agency Incident Hotline on 0800 80 70 60. The Environment Agency Drought Team can be contacted by emailing drought_THM@environment-agency.gov.uk or via Environment Agency general enquiries 03708 506 506.

/ENDS.