Urban waste water
At SEPA, our vision is for towns and cities to use nature-based, blue-green solutions. This will:
- help strengthen resilience to the intense downpours cities face due to climate change
- minimise the risk of polluting sewage spills by keeping rainwater out of sewers
- create fantastic places for people to live and work
Improving urban waters
Scotland’s urban waters - rivers, burns and coastal waters in towns and cities - are under pressure from sewage discharges, litter and pollution. In 2021, SEPA made it clear that we need to take bold action to deal with the most harmful impacts more quickly and effectively. This means moving beyond business as usual and improving urban waters now while planning long‑term, sustainable solutions for the future.
Improving urban waters cannot be done by Scottish Water alone. It requires coordinated action from SEPA, the Scottish Government, local authorities, businesses and the public.
Current problems affecting urban waters
In recent years, new and growing concerns have emerged around the quality of urban water, including:
- microplastics entering rivers and seas through sewage
- antimicrobial resistance, which can spread through wastewater
- increased wild swimming, meaning people are more directly exposed to pollution
- sewer-related litter, such as wipes and plastics, ending up in the environment
Current legislation doesn’t encompass all of these issues. SEPA has recognised that regulation and policy need to evolve to deal with these challenges and has committed to working with partners, NGOs and communities to shape long‑term solutions, including reducing spills and eliminating sewage-related litter.
River Basin Management Planning (RBMP)
The River Basin Management Plan 2021–2027 sets the overall goals for improving Scotland’s water environment. It identifies actions needed to protect and improve rivers, lochs, groundwater and coastal waters.
Urban water improvements are a key part of the RBMP, and Scottish Water is a responsible authority for delivering many of these actions.
Find more information about RBMP.
Our work with Scottish Water on the Improving Urban Waters Routemap
Scottish Water owns, operates and maintains public sewerage systems. They are responsible for:
- removing and treating wastewater
- managing blockages, collapses or capacity issues in public sewers
- reducing the risk of flooding from public sewerage systems
In 2021, SEPA wrote to Scottish Water setting out expectations and timelines for a clear plan to improve urban waters.
In December 2021, Scottish Water published its Improving Urban Waters Routemap, which outlines:
- where improvements are needed
- what actions Scottish Water will take
- where partnership working is required
- the scale of investment needed
SEPA welcomed the routemap and confirmed it would monitor progress, work with stakeholders on long-term ambitions, and use regulatory powers if necessary to improve urban waters.
What the routemap aims to deliver
Scottish Water, working with partners, committed to:
- improving water quality in line with RBMP goals
- increasing monitoring and transparency
- significantly reducing sewer-related litter
- reducing pollution spills from the sewer network
What is a combined sewer overflow (CSO)?
Combined Sewer Overflows (CSOs) are safety valves in the sewer system. They are designed to release excess water during heavy rain to stop sewers backing up and flooding homes, streets and businesses. When too much rainwater enters the system at once, CSOs allow diluted wastewater to overflow into nearby rivers or the sea to protect property and public safety.
Why are CSOs overspilling more often?
Many CSOs now spill more often than intended because the sewer system is under increasing pressure. This is due to:
- more water in the system than it was designed for, caused by:
- new housing and business growth
- gardens and green spaces being paved over
- heavier and more intense rainfall due to climate change
- problems in the sewer network, such as the build-up of silt or groundwater leaking into pipes
- blockages, often caused by items that should not be flushed, like wet wipes, fats and oils
There are around 35,000 blockages each year in Scotland. Together, these issues mean CSOs spill more frequently, even during relatively small storms.
What are the impacts of CSOs?
Sewage spills can sometimes cause sudden pollution, usually when sewers become blocked. Serious incidents are rare in Scotland. Each year there are typically fewer than 10 significant incidents and around 200 minor incidents reported.
Many sewage spills release litter such as wipes and plastics into rivers and coastal waters.
Around 80% of CSOs in Scotland do not have screens, so litter can pass straight into the environment during rainfall. Even where screens are fitted, they are not perfect and usually only capture up to 90% of debris.
Over 600 CSOs are currently known to cause unacceptable levels of sewage litter. As spills become more frequent, better screening and other solutions are needed.
A small number of CSOs spill so often that they cause long‑term pollution over stretches of river. This can reduce oxygen levels or increase ammonia, harming fish and wildlife.
24 CSOs are officially identified in the River Basin Management Plan 2021–2027 as affecting river water quality.
CSOs can release bacteria that affect water safety. These impacts are closely monitored.
We take action to protect designated bathing waters and shellfish waters. This applies to 85 protected sites across Scotland.
Some pollutants in sewage are not yet fully understood or regulated, including:
- microplastics and plastics
- medicines, hormones and other chemicals
- viruses
- antimicrobial resistance
Most of these are not currently assessed in the River Basin Management Plan, but they are growing concerns for both freshwater and marine environments.
Improving urban sewage and CSOs
Overview of improvements made with Scottish Water
Over the last 20 years, SEPA has worked with Scottish Water to improve how sewage is collected and treated across Scotland. From 2010 to 2021, Scottish Water was required to upgrade 279 sewer overflows and 104 wastewater treatment works that were causing pollution. These improvements were prioritised in Scottish Water’s investment programmes during that period.
Results of improvements
Thanks to these upgrades, Scotland’s water environment is now in its best condition to date, with 87% of rivers, lochs and coastal waters rated good or better.
However, concerns about sewer spills have grown in recent years. More people now value and use their local waters, including for outdoor and wild swimming. At the same time, climate change and incorrect items being flushed are putting extra pressure on the sewer network.
Future plans
The River Basin Management Plan 2021–2027 recognises that more needs to be done, particularly in towns and cities. The focus is now on improving urban waters and moving towards a circular economy approach to managing wastewater in Scotland. This supports SEPA’s long‑term vision for a healthier, more resilient water environment.
Recommendations from Environmental Standards Scotland
Environmental Standards Scotland (ESS) published a report in September 2024, which contained 3 recommendations for SEPA. These were:
to make data in relation to wastewater spills and environmental pollution available to the public
to review and update authorisations and guidance in line with best practice
to identify all instances of overflows which happen in dry weather, and prioritise these for investigation and improvement
We responded in March 2025 and continue to provide regular updates:
We also compile storm overflow data with Private Finance Initiative (PFI) and Scottish Water operated authorisations.
Overflow events data reported to SEPA, 2020 to 2025 (MS Excel, 6 MB).
The data will be updated annually, with the next publication due in 2027.
Antimicrobial Resistance (AMR) in the environment
Urban waters and sewer systems are identified as key pathways for antimicrobial resistance to enter rivers, burns, and coastal waters.
SEPA’s actions on AMR in urban waters and CSOs include:
recognising AMR as a significant urban water pressure
driving reductions in CSO spills and wastewater impacts
expanding environmental monitoring of resistant organisms
applying a One Health regulatory framework, linking environmental quality to human and animal health
using AMR to support blue‑green infrastructure and sewer separation