We’re proposing major investment to improve drinking water and wastewater services on the Isles of Scilly.
You can find out more about our plans to improve drinking water services here.
Our improvements to wastewater services will protect water quality and meet the challenges of the future.
Our aims include:
- Protecting water quality and improving resilience
- Increasing treatment capacity on St Mary’s to support growth
- Connecting more properties to the sewer network.
Two drop-in events are being held on St Mary’s where you can find out more about our plans to improve wastewater services and speak directly with our team.
16 June
3pm to 7pm – St Mary’s Methodist Church, Hugh Town
17 June
3pm to 6pm – Old Town Inn, Old Town
You can drop in at any time during the sessions to ask questions, understand what’s planned and find out what it means for you.
Current position and next steps
Our initial plans have been improved to ensure they deliver the right long-term plan for the islands as well as minimising disruption to residents and impact on local heritage.
We’ve worked with partners and regulators to put interim improvements in place while we reviewed and amended the proposals first set out in 2024.
This page provides information about proposals for wastewater improvements, details of drinking water proposals will be updated later in 2026.
Isles of Scilly programme
Please be aware these dates are subject to planning applications.
| Date | Activity |
| Spring to summer 2026 | Public drop-in events will be held to support community engagement. A planning application will be submitted for a new fine-screening plant and upgrades at Bishop and Wolf. |
| August 2026 | Preparation works begin on site (mobilisation). |
| September 2026 | Construction starts on the new fine-screening plant and new sewer connections for Hugh Town, Old Town and Telegraph. |
| April to June 2027 | Long sea outfall drilling works. |
Proposals
Improvements are being made to how wastewater is collected, transferred and treated on St Mary’s to provide a more reliable and environmentally sustainable service.
The updated plans combine a new facility with upgrades to existing infrastructure and new connections, reducing disruption while delivering long-term improvements.
The proposals include:
- Refurbishment of the existing Bishop and Wolf pumping station within its current footprint.
- Construction of a new fine screening plant next to the existing Old Town site.
- A new underground sewer main connecting Hugh Town to Old Town.
- The release of screened wastewater through a new long sea outfall under Porth Minick.
This approach has been selected because it:
- Reduces disruption for residents and businesses.
- Minimises environmental impact.
- Avoids work near the Garrison historic monument.
- Provides a practical long-term solution for the islands.
Longer term, First Time Sewerage schemes are also being developed to connect homes on St Mary’s, St Martin’s, St Agnes and Bryher to a sewer network.
Proposed works diagram
Fine screening process at Old Town
A new pre-treatment facility is proposed alongside the existing site near Old Town. This will screen wastewater before it is discharged through a new long sea outfall.
Wastewater will pass through screening to remove larger and smaller solids before discharge.
After screening, wastewater will be released through an outfall pipe running beneath the seabed from Porth Minick.
The proposed approach avoids the need for secondary treatment, which would have a significantly greater impact on the environment and local community with limited additional benefit to water quality.
Compared with this approach, secondary treatment would:
- Use around 75% more energy.
- Generate 21 times more carbon emissions.
- Produce almost 2,600 tonnes of waste – mostly sewage sludge – that would need to be transported to the mainland via the quay in Hugh Town.
- Require significantly more land.
- Take more than twice as long to build.
Modelling shows the design will protect local water quality to a high standard.
Work is ongoing with the Environment Agency to secure the required permit, and a planning application will be submitted to the Council of the Isles of Scilly to meet the regulatory deadline of September 2027.
Long sea outfall
A new long sea outfall will be installed to release screened wastewater offshore.
A long sea outfall is a pipe that carries wastewater out to sea, where it is released at a suitable depth and distance from the shore. This allows it to disperse naturally without affecting beaches or water quality.
The outfall will:
- Run for around 470 metres from Porth Minick.
- Be installed underground and beneath the seabed.
- Release water at a depth of around 20 metres.
- Discharge only from the final 10 metres of the pipe.
To connect the Old Town site, a new underground sewer will be installed through Trench Lane and into fields to the south of Old Town. This will be around 500 metres long, depending on the final route.
The outfall will allow the existing Morning Point outfall to be taken out of use, avoiding further work near the Garrison and reducing long-term environmental impact.
Several locations were assessed, including repairing or replacing the current outfall. The preferred option provides the best balance of environmental protection, buildability and cost.
Modelling using a range of wind and tidal conditions shows the outfall will:
- Protect local water quality to a high standard.
- Avoid negative impacts on nearby beaches and coastal waters.
- Protect nearby water sources.
The outfall will be installed using horizontal directional drilling, a trenchless method that avoids the need for open trenches along the beach or seabed. This reduces excavation and protects sensitive environments.
Open trench methods will be used to connect the sewage system to the outfall. Both pipes will be approximately 315mm in diameter and made from high-performance polyethylene (HPPE), a durable material used for underground and marine pipelines.
Improving wastewater services
Improvements are being made to how wastewater is collected, transferred and managed on St Mary’s, including a new treatment facility, upgraded infrastructure and new connections. Together, these changes will provide a more reliable service and support future growth.
Protecting the environment
The proposals will protect local water quality and minimise impacts on the natural environment and the islands’ heritage.
Managing construction and disruption
Work will be carefully planned to minimise disruption to residents, businesses and visitors. A temporary welfare compound will be set up on St Mary’s to support construction and reduce pressure on local accommodation.
Bishop and Wolf pumping station
The Bishop and Wolf pumping station will be fully refurbished to improve reliability and increase capacity, while remaining within its existing footprint.
This work will include the installation of new pumps, upgrades to control equipment, and improvements to make the site easier and safer to operate and maintain.
A temporary working area will be set up on the nearby green to support construction. This will be used to store equipment and materials.
The working area will be in place for a limited period and will be returned to its previous condition once the work is complete.
Hugh Town to Old Town connection
As part of the improvements, a new underground rising main will be installed to connect Hugh Town to the Old Town site. A rising main is a pumped pipe that moves wastewater between locations.
The new main will:
- Be around 1.5 kilometres long.
- Be approximately 250mm in diameter.
- Be installed using trenching methods.
The new rising main will be installed using open trench construction methods. The work is expected to take around six months to complete, depending on ground conditions.
Work will be planned outside peak tourist seasons wherever possible to reduce disruption for residents and businesses.
Details of temporary laydown and storage areas are still being confirmed.