How much raw sewage is released into rivers and the sea, and what are the rules?

Water companies released record spills of raw sewage into the sea and rivers in England in 2023.

Rules allow a limited discharge of excess sewage during periods of excess rain, but there is also evidence of "dry spills", which can damage 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 it was "unacceptable", but that the record levels were due to heavy rain and increased data collection.

However, the Environment Agency said that increased rainfall does 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.

Usually, all the waste is carried 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.

This is known as combined sewer overflows (CSOs) and is allowed.

However, there is evidence that some water companies also spill sewage when it is not raining.

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

A BBC investigation suggested there were 388 potential "dry spills" by Thames, Wessex and Southern Water in 2022.

Water companies which are found to have breached the rules by spilling on dry days or failing to meet other conditions can be fined or prosecuted.

The government announced a plan to improve water quality in April 2023.

As part of this, it said polluters could face unlimited fines in the future, which was confirmed in July 2023.

The government says penalties from water companies will be re-invested into a new Water Restoration Fund which aims to improve water quality.

But then-Environment Secretary Therese Coffey said there was "no way we can stop pollution overnight", given the major changes needed to the water system.

Industry body Water UK has announced plans 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.

Swimmers are warned to stay away when untreated sewage is discharged into the sea.

The contaminated water could lead to serious illnesses.

Risks include gastrointestinal illnesses, or stomach bugs, which may cause diarrhoea and/or vomiting, as well as respiratory, skin, ear and eye infections.

Rowers taking part in the 2024 Boat Race between Oxford and Cambridge in London have been warned not to enter the Thames after high levels of E. coli were found.

Between May and September each year, the Environment Agency measures the water quality at several sites across England either weekly or daily, and issues pollution risk forecasts.

You can search its website by location.

There are similar websites where you can find out about beaches and bathing water in Scotland, Wales or Northern Ireland.

Campaign group Surfers Against Sewage has created an interactive map showing pollution risk warnings along the coast and rivers.

Sewage spills have only been routinely monitored for a few years, so it is difficult to tell 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 surface waters in England achieved "good" ecological status, including:

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

In Scotland, 63% of surface waters are classed as having "good" ecological status.

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

In August 2022, three French members of the European Parliament said they had asked European Commission to stop the UK polluting the Channel and the North Sea.

Since Brexit, they said the UK had "chosen to lower its water quality standards".

The UK is no longer bound by EU environmental legislation. But those laws did not directly regulate the frequency or number of sewage discharges.

According to Friends of the Earth, the UK's Environment Act 2021 - which replaced the EU laws - brought "some useful changes" which included "efforts to stop companies filling our waterways with sewage".