Tackling the Crisis in UK Water Quality: Prospects for Improvement

Researchers from the Centre for Environmental Policy are driving urgent calls for reform in the UK water sector.

In 2024, English water companies discharged untreated sewage into rivers and seas for a record 3.614 million hours, a slight increase from the 3.606 million hours recorded in 2023. Sewage spills had more than doubled in 2023, according to the Environment Agency, with 3.6 million hours of spills compared to 1.75 million hours in 2022.

The new Labour government assert that the previous Conservative government “turned a blind eye and weakened rather than strengthened regulation” of the water industry. Labour have said that they "will put failing water companies under special measures to clean up our water."

The new government has also pledged to "give regulators new powers to block the payment of bonuses to executives who pollute our waterways and bring criminal charges against persistent law breakers" and "impose automatic and severe fines for wrongdoing and ensure independent monitoring of every outlet."

In response to these, the Tackling the Crisis in UK Water Quality: Prospects for improvement under a new Labour government symposium took place on Tuesday 11 March 2025, organised by the Public Policy Exchange.

It offered stakeholders, including central and local government, regulators, water companies, environmental charities and campaigners, the opportunity to examine the state of UK seas and waterways, assess the plans proposed by the new Labour government to fix the crisis in UK water quality, and to evaluate the reforms needed to improve water management, upgrade infrastructure, tackle pollution, strengthen regulation and place the water industry on a sustainable, long-term footing for the benefit of all.

Professor Nick Voulvoulis from the Centre for Environmental Policy at Imperial was a key speaker at the event (and below some the main points of his talk).

The UK's sewer systems are some of the oldest in Europe. They have been designed to collect both wastewater from domestic, commercial, and industrial activities as well as stormwater runoff from pervious paved surfaces and roofs, and transport them to wastewater treatment works for treatment.

In times of heavy rainfall, the flow can increase significantly, and sewerage systems have been designed to relieve some of the excess flow at combined sewer overflows (CSOs). Think of CSOs like an emergency relief valve which discharge untreated sewage directly into waterbodies when sewer systems get overwhelmed during heavy rain or snowmelt.

Treatment plants must treat a minimum amount of wastewater at any given time, known as the 'flow to full treatment', as specified in their environmental permit. This minimum is typically set at three times (or six times for smaller works) the 'dry weather flow', which is all flow in a sewer that is not directly caused by rainfall. This gives them enough capacity to treat variations in wastewater flow (the peak flow from the increased water usage in the morning, as people wake up and use the toilet, shower, etc. and another again in the evening after work or school), plus any additional flows from light rainfall.

Research at CEP has shown the chronic under capacity of the English wastewater systems as a fundamental cause behind the increased frequency and duration of sewage overflows. This sewage discharge has attracted increased media and political coverage over the last several years. Most wastewater treatment plants are now treating a significantly higher volume of flow than they were designed and built to accept, and CSOs are used as a way to manage the under capacity of the systems.

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The increased frequency of CSO spills can result in detrimental effects for the receiving waterbodies. Discharges of untreated wastewater from CSOs can lead to oxygen depletion or increases of pollutant concentrations in the receiving waters. Municipal wastewater contains microbial pathogens, total suspended solids, nutrients, microplastics and several toxic chemicals including persistent organic pollutants, heavy metals and other contaminants from industrial and commercial activities, potentially having dire consequences when discharged in the environment untreated. CSOs can therefore pose risks to public health, contamination of shellfish, and negative effects on aquatic wildlife, leading to decreased water quality and negative impacts to wildlife.

CSO spills are a systemic issue across all water companies, as it is their responsibility to maintain sewerage assets and upgrade them to deal with any additional flows as part of the water industry investment rounds which occur every five years. These assets include the sewerage network as well as treatment works, but clearly investment has not been keeping pace with the increased demand nor in some cases with the deterioration of these assets.

While water companies are directly responsible for CSO discharges, there has also been growing scrutiny on Ofwat's role in regulating and enforcing standards, its oversight of CSO usage, its approach to penalties, and whether it has adequately ensured sufficient investment in infrastructure.

Labour Government response

The Water (Special Measures) Act was introduced into Parliament on 4 September 2024 and received Royal Assent on 24 February 2025. The Act strengthens the power of the water industry regulators such as the Environment Agency and Ofwat, with enhanced powers to hold water companies accountable for environmental damage.

In sum they can:

• impose stricter penalties and take swift action against negligent companies;
• bring criminal charges against executives and use penalties that may extend to imprisonment for those obstructing investigations;
• strip companies of the ability to award bonuses to their executives unless they meet stringent environmental standards and provide reliable services to consumers;
• issue automatic penalties to streamline enforcement actions;
• authorise independent monitoring of sewage outlets, requiring that real-time data on discharges be made publicly available within an hour;
• require annual Pollution Incident Reduction Plans, enabling both regulators and the public to scrutinise company progress in curbing pollution incidents.

The revised EU Urban Wastewater Treatment Directive

Europe's ageing wastewater systems face similar problems. With approximately half of the sewer systems in the European Union being combined, CSOs are a significant source of pollution. The EU Urban Wastewater Treatment Directive was recently revised to address some of these concerns. The revised directive entered into force on 1 January 2025 and aims to protect human health and the environment from the effects of untreated urban wastewater.

It aims to improve water quality through stricter water treatment and the inclusion of new pollutants; strengthen the EU’s polluter-pays principle by ensuring that those responsible for pollution bear the costs of remediating it; advance circularity through water reuse and the recovery of valuable resources from wastewater; address climate change through GHG emission reduction of treatment plants and urban adaptation to heavy rainfall; and ensure access to sanitation for all, particularly the most vulnerable and marginalised.

The aims of the Directive are to monitor sewage overflows and have wastewater plans in place, aiming to cut pollution, especially microplastics, so overflows make up no more than 2% of annual sewage by 2039 or 2045 (depending on city size). Plans must prioritise green infrastructure (e.g., permeable pavements, rain gardens) to reduce stormwater volumes entering sewers, minimising CSO frequency and impact.

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Overall, the revised Directive represents a significant step forward in addressing the persistent challenges of water pollution, environmental degradation, and public health risks posed by untreated wastewater. However, achieving the Directive’s goals will require accelerated investments in wastewater infrastructure, and a collective commitment from Member States to prioritise water quality on their political agendas. Its success will depend on how effectively these investments and commitments are implemented, particularly in the face of current global challenges.

The Way Forward

Asked about the way forward, Professor Voulvoulis , said: "A modern and robust water infrastructure is vital to the country’s economic development as it secures not only the supply of water but also prevents the spread of illness and diseases, fosters economic growth, and ensures a higher living standard."

The water industry has an important role to play as a responsible custodian of the water cycle.

We need a policy system that shapes and influences the broader enabling environment and conditions for the uptake of sustainable practices leading to the sustainability transformation of urban water systems.

For more, please read:

• System thinking for sustainable water management: the use of system tools in sustainability transitions
• Combined sewer overflows: relating event duration monitoring data to wastewater systems' capacity in England
• Systems thinking for the sustainability transformation of urban water systems
• Transitioning to a sustainable circular economy: the transformation required to decouple growth from environmental degradation
• Systems thinking as a paradigm shift for sustainability transformation