How much raw sewage is released into rivers and the sea?

The water industry regulator Ofwat has proposed fines totalling £168m for Thames Water, Yorkshire Water and Northumbrian Water as part of its largest-ever investigation into sewage spills.

Water companies can release untreated sewage into rivers and seas when it rains heavily to prevent homes being flooded, but Ofwat said it had found cases where sewage was being released prematurely.

Without full treatment the released sewage can cause more damage to the local environment and pose a health risk to swimmers.

Sewage spills into England's rivers and seas by water companies more than doubled in 2023.

According to the Environment Agency, there were 3.6 million hours of spills, compared to 1.75 million hours in 2022.

Water UK, the industry body for sewerage companies, said this was "unacceptable", but argued that the record levels were due to heavy rain and increased data collection.

However, the Environment Agency said that increased rainfall did not override water companies' responsibility "to manage storm overflows in line with legal requirements".

Some environmental charities blame water companies for a failure to fix leaky pipes and other damaged infrastructure - and criticise the regulator for not forcing them to act.

Most of the UK has a combined sewerage system, meaning that both rainwater and wastewater - from toilets, bathrooms and kitchens - are carried in the same pipes.

Wastewater is usually sent to a sewage treatment works.

But capacity can sometimes be exceeded during heavy rainfall, especially if dry ground cannot quickly absorb large quantities of water.

This could lead to inundation of sewage works and potential flooding of homes, roads and open spaces.

The system is therefore designed to overflow occasionally, and discharge excess wastewater into the sea and rivers from combined sewer overflows , external(CSOs)

However, according to Ofwat, some water companies have been "routinely releasing sewage" outside times of heavy downpours as a result of failing to managing their wastewater treatment plants.

Without rainwater to dilute the waste, this can lead to higher concentrations of sewage entering waterways - and is therefore illegal.

It its own investigation earlier this year the BBC found 6000 potential dry spills by England's water companies in 2022 - including during the record summer heatwave when people were cooling off in England's rivers and seas.

In April 2023 the previous Conservative government announced a plan, external to improve water quality.

As part of this, it said polluters could face unlimited fines in the future, external which would be re-invested into a new Water Restoration Fund which aims to improve water quality.

Six months later Water UK, the industry body, announced plans on behalf of its members to almost double spending to pay for upgrades and cut sewage discharges.

It said this would be the "most ambitious modernisation of sewers since the Victorian era", but that customer bills would have to rise by £156 a year to cover the cost.

Since taking office in July the Labour government has announced a series of proposed reforms, promising consumers higher compensation for sewage failures and the power to hold executives to account.

It plans to introduce new measures to ensure that money earmarked for investment and improvements cannot be diverted to pay salaries or dividends.

Speaking in response to Ofwat's proposed fines, Secretary of State for Environment, Food and Rural Affairs, Steve Reed said: "We will outline further legislation to transform and reset our water industry and restore our rivers, lakes and seas to good health."

In May 2024, a team of the UK's top engineers and scientists warned of the growing public health risk from human faeces in the country's rivers, and called for more regular testing.

The presence of faeces can expose people to bacteria such as salmonella and E.coli, which cause diarrhoea and vomiting, or viruses like hepatitis A which can lead to liver infection.

Also in May, thousands of residents in Devon were told to drink bottled water after their supply was contaminated with the cryptosporidium parasite - possibly as a result of a faulty valve on private land. Consumption of the parasite can cause prolonged diarrhoea.

Every week between May and September, the Environment Agency measures the water quality at "bathing sites" across England, and in some places it issues daily pollution risk forecasts.

You can search its website, external by location. There are similar websites, external where you can find out about beaches and bathing water in Scotland, Wales or Northern Ireland.

But outside of these times and locations regularly testing for organisms carrying faecal-oral disease is not carried.

By the end of this year all water companies are expected to have maps showing near real-time discharges at their storm overflows to keep the public better informed.

Sewage spills have only been routinely monitored for a few years, external, so it is difficult to tell exactly how they have changed over time.

However, overall water quality has been monitored for decades. This also accounts for other sources of pollution, such as agriculture.

In May 2023, the Environment Agency said that 16% of assessed surface waters in England achieved "good" ecological status, external, including:

Water quality is generally higher in other parts of the UK, external.

In Scotland, around two-thirds of surface waters are classed as having "good" ecological status.

In Wales the figure is 40%, and in Northern Ireland 31%.