A future vision for Windermere that is fed only by the rivers, streams and springs that flow off the land is the goal of the
Only Rainwater into Windermere project.
A ‘one and done’ solution unifying the wastewater system across the entire catchment, the project would see a UK-first, 138-kilometre underground network transferring wastewater away from Windermere to be treated at a new, state-of-the-art treatment works.
ORiW tackles a major controllable cause of nutrient enrichment in Windermere at source, helping to protect the health, appearance and ecology of the lake for generations to come, securing Windermere in its rightful place at the heart of a thriving National Park.
Incremental infrastructure upgrades will mean repeated investment, construction and disruption every five years. ORiW offers a transformational, long-term alternative – breaking the cycle of reactive spending and delivering lasting environmental benefits that conventional upgrades cannot achieve.
Rising temperatures, more intense rainfall and increasingly extreme weather will place pressure on Windermere and its wastewater infrastructure. ORiW addresses these challenges at catchment scale, building the resilience needed to protect the lake for decades to come.
Modelling indicates that only a ‘no sewage’ scenario will reduce harmful algal bloom exceedance days to zero by 2079. ORiW provides a route towards this level of ambition, going beyond simply managing pollution to fundamentally changing Windermere’s ecological future.
Windermere is central to a tourism economy attracting approximately 17.7 million visitors annually. Continued water quality concerns therefore represent a long-term risk to Windermere’s visitor economy, with modelling indicating that deterioration could result in annual economic losses of up to £122.5 million.
Sustained public campaigning, national attention and landmark citizen science initiatives reflect a clear public demand for a step-change in how Windermere is protected and restored. ORiW provides an opportunity to respond with a bold, credible and lasting commitment – restoring public confidence and protecting one of the nation’s most treasured natural assets.
Breaks the cycle of repeated disruption from incremental investments, creating lasting environmental, social and economic value.
Wastewater returned to the environment at the highest possible standard, downstream of Windermere, removing any discharges into the lake.
Up to 138km of catchment-wide network, including 77km of network for first-time sewerage, 42km of rising main and 19km of tunnel network bringing together public and private wastewater through one coordinated system.
A solution that can be delivered at pace, create high-quality jobs for the local economy and leave a lasting legacy of a Cumbrian skills academy.
Approximately 12,800 people could benefit from connection to public sewerage services for the first time.
Surface water separation and sustainable, nature-based drainage systems to support greener rainwater management.
The system is designed to remain effective beyond 2100 under a range of future climate scenarios and make the lake resilient to change.
Receiving over 2.5 metres of rain annually, with a significant proportion of combined sewers, the catchment requires circa £2.5 billion investment in the next 100 years. ORiW delivers faster, better outcomes within seven years.
Removing wastewater, the most significant controllable source of nutrients, supports a cleaner, healthier lake for generations to come.
100-year solution setting new standards for freshwater ecology in the UKA coordinated, catchment-scale restoration programmeDiverting treated and untreated wastewater inputs and tackling highways run-off at sourceFuture-proofing Windermere against the pressures of climate changeSecuring the long-term ecological recovery of England’s largest natural lake
Approximately
12,800
people with access to public sewerage for the first time
Up to
138km
of new network
Up to
75%
increase in wastewater infrastructure
35km
of highway drainage intercepted
£7.5bn
economic benefit over the life of the asset
Creating jobs and supporting
£2.4bn
value to the tourism economy in the Lake District National Park
Existing United Utilities service coverage and wastewater treatment works around Windermere.
Estimated septic-tank density shown in hexagons with 500 metre sides, alongside non UU outfall points. Counts range from 1-10 to 41-90 per hexagon.
Illustrative gravity tunnel and rising-main routes connect the common elements to the Leven and Ulverston treatment and outfall options.
Creating a coalition of stakeholders aligned around a single vision to protect the future of the lake.
Establishing the facts, understanding the problem and opportunities and drawing on international expertise, ensuring solutions are transformative and designed for the next century and not just today.
Critically evaluating options to establish the preferred solutions that deliver the greatest environmental, social and economic value to safeguard the future of Windermere.
The launch of the feasibility report to deliver the ORiW ambition.
Securing a shared commitment to progress the ORiW ambition into the next stage. This milestone confirms partner alignment, governance support, funding confidence and strategic agreement to advance the preferred ways forward.
Advancing the preferred ways forward into a fully defined and deliverable scheme.
Once approvals are secured, the programme will move into procurement and mobilisation. This includes engaging the supply chain and appointing delivery partners based on technical capability, cost, quality and a shared ambition to achieve the ORiW vision.
Constructing the infrastructure required to achieve the ORiW ambition. Delivery will need to be coordinated, innovative and sensitive to the importance of working within a nationally significant landscape.
The ORiW Business Case chapter documentation comprises the following documents:
Business Case Document Guide and Programme Background
Business Case Executive Summary
Strategic Case
Economic Case
Economic Case Appendix
Commercial Case
Financial Case
Management Case
Business Case Glossary
These documents should be read together, as each addresses a different aspect of the programme.
The Business Case chapters present an assessment of evidence to support the ORiW feasibility study. They are structured around the HM Treasury Five Case Model and apply Green Book principles proportionately. Because the programme is at feasibility stage, ahead of a Strategic Outline Case, they follow the guidance in a way which is proportionate to the current stage of project development.
Purpose of the Business Case chapters: The chapters assess whether there is a credible case for intervention beyond currently committed investment, identify a feasible shortlist of options and recommend a most preferred option for further investigation. They are intended to inform future decision-making, stakeholder engagement and consultation; and do not provide a final design or implementation plan.
Use of evidence and proportionality: The chapters make best use of the evidence available up to September 2026, and the level of analysis is proportionate to the stage of assessment. At this stage, the purpose is to compare strategic approaches and identify the best-performing options in terms of value for money, resilience and deliverability, rather than to define a final engineering solution. The analysis relies in part on data and modelling provided by third parties. Where primary evidence was not available, the analysis draws on published studies, value transfer, expert judgement and stated assumptions, which are set out in the relevant chapters and appendices. Costs, designs, delivery models, environmental assessments and programme assumptions will continue to evolve as further evidence becomes available.
What has been developed, and what has not: The chapters identify a most preferred way forward to achieve ORiW based on available evidence. This is not a final investment decision, planning application, funding commitment or approval to proceed. Further design, assessment, stakeholder engagement, consultation, customer research, regulatory approvals and business case stages would be needed to inform any final decision. Publication is intended to support transparency and informed discussion.
Stakeholder positions: The chapters contain inputs from a stakeholders represented on the ORiW Steering Group, but they do not represent the position of any stakeholder.
Cost estimates: Costs are feasibility-level estimates to AACE class 4 accuracy; which typically have an uncertainty range of -30% to +50% and include allowances for risk and optimism bias. They are not budgets, tender prices or outturn costs. They should not be used for project budgets.
Understanding the benefits presented: A significant majority of the benefits assessed in the Economic Case are environmental and social rather than direct financial returns. They reflect estimates of the value society places on environmental quality, recreation, wellbeing, amenity and the protection of nationally important natural assets. They are not revenues generated by the programme.
How to interpret the Benefit-Cost Ratio (BCR): A BCR compares estimated monetised benefits with estimated costs. A value above 1.0 shows that estimated benefits exceed estimated costs under the assumptions used. Consistent with HM Treasury Green Book guidance, value for money also takes account of non-monetised impacts, distributional effects, risk, resilience deliverability and alignment with objectives.
Valuation uncertainty: Amenity and environmental values are transferred from studies of other locations. They are indicative at this stage.
Programme timing: Dates used in the appraisal give a consistent basis for comparing options and should not be read as committed delivery dates. Actual timescales will depend on approvals, consents, funding, procurement, land access, design development and other programme dependencies.
Environmental modelling: The modelling gives evidence-based indications of how different scenarios may affect lake condition and water quality. It supports option comparison for this stage, but it is not a precise forecast of future environmental outcomes.
Caveats, assumptions recommendations for further work: The chapters contain caveats, assumptions and recommendations for further work to be addressed as the project progresses.
Redactions: Some commercially sensitive information has been removed before publication.
Engineering, environmental and economic analysis for the ORiW feasibility study
has been carried out by Jacobs and Mott MacDonald.
