FactCheck: why do water companies spill sewage into rivers and seas and how does UK water quality compare to other countries?

The water quality of the UK’s rivers, seas and lakes has been in the spotlight in recent years, with campaign groups calling on the government, regulators and the water companies to “take action” against sewage spills.

So why are water companies allowed to spill sewage and how does our water quality compare to other countries?

FactCheck takes a look.

Why do water companies spill sewage into rivers and seas?

Water companies are sometimes allowed to spill sewage into open water following heavy rainfall to prevent the system becoming overloaded, using relief valves called “storm overflows” to release extra rainwater and wastewater into rivers or seas.

But campaigners have long said that these spills are happening too often.

According to the latest data from the Environment Agency, there were just over 300,000 “monitored spill events” in 2022 in England.

Although still high, this was actually down 19 per cent compared to 2021, and 25 per cent lower than 2020.

But, it’s still nearly 24 times higher than in 2016 and more than nine times higher than 2017.

Ali Morse, water policy manager at The Wildlife Trusts, told FactCheck: “The public rightly want to see urgent action on the pollution which continues to place the UK’s rivers at grave risk.”

Though she also pointed to other problems in the water system. The impact of sewage spills is “dwarfed by the harm caused by treated wastewater and farm pollution,” she said.

This is echoed by Dr Tanja Radu from Loughborough University’s water engineering and development centre, who said: “The overall water quality is heavily impacted by the raw sewage release, along with the contribution from agriculture, urban runoffs, and climate change.”

A Defra spokesperson told FactCheck the department’s farming schemes “are providing significant funding to reduce agricultural run-off” and the government’s Plan for Water is “tackling every source of pollution and ensuring swift enforcement action is taken against those who break the rules”.

Experts often point to the state of our sewers and growing population as reasons behind sewage spills.

Dr Radu noted that “dated infrastructure and the increased pressure on wastewater treatment plants due to the increase in population are often blamed for the frequent raw sewage release.”

She said “the lack of investment in the infrastructure means that the water companies often rely on the combined sewer overflow (CSO) network, even though this is to be used only during incidents such as extreme rainfall.”

How does our water quality compare to other countries?

The UK is one of ten European countries that share the top Environmental Performance Index (EPI) ranking for the cleanest drinking water worldwide.

Though only 16 per cent of England’s surface water bodies – like rivers, seas and lakes – currently reach Good Ecological Status (GES) or higher. In Scotland, this is 48 per cent. It’s 44 per cent in Wales, and 31 per cent in Northern Ireland.

Ecological status is assigned by using various water, habitat and biological quality tests, such as pollution by toxic chemicals. A “good” status is defined as “slight change from natural state as a result of human impact”.

The Water Information System for Europe says that across the continent, around 40 per cent of surface water bodies are in good or high ecological status, particularly the northern Scandinavian region and Scotland, as well as Estonia, Romania, Slovakia and in the Mediterranean region.

For bathing water sites, which are measured differently from ecological status, 86 per cent per cent were of excellent quality in 2022, according to the European Environment Agency (EEA). The top performers were Cyprus, Austria, Greece and Croatia – where 95 per cent were graded excellent.

Separate data published by the UK government in 2023 shows that out of 423 bathing waters in England, 66 per cent were classified as excellent (which means it’s the highest, cleanest water quality), though these figures are not directly comparable to the EEA figures.

It’s worth noting that the frequency with which some water quality is recorded has also now changed since Brexit.

Dr Radu said that “whilst in the European Union, our [England] waters were monitored on an annual basis under the Water Framework Directive”.

But since leaving the EU, “we have now moved to reporting every three years – with the next full assessment expected in 2025”.

(Image credit: Maureen McLean/Shutterstock)