Experts say putrid stench shows overhaul of sewers is needed – like the one prompted by the Great Stink of 1858
London was “reeking with ineffable and intolerable horrors” after weeks of temperatures exceeding 30C and minimal rainfall. This was Disraeli’s description of the Great Stink of 1858, but something similarly disgusting has been happening this summer.
Once again, an exceptionally hot and dry spell has exposed the putrid stench of untreated human waste.
“There’s been a bad smell around for weeks,” said Simon Birkett, the founder and director of Clean Air in London. “After campaigning for 20 years my nose is a bit of connoisseur for air pollution, and there really is a stench.
“If you go anywhere near a stormwater drain you can almost feel it wafting up. The general public are not going to forget the summer of 2026 and one of the symptoms is this toxic stench.”
Drainage experts say this summer’s stench should prompt a radical overhaul of an outdated system, just as the Great Stink ushered in a new sanitation in the Victorian era.
Prof Barbara Evans, the chair of public health engineering at Leeds University, likened the current sewer network to a “giant intestine”.
She says: “In our guts we have a massive microbiome designed to break down organic materials. When we put all that plus the carbon, nitrogen and phosphorus that’s in our gut into the sewer, the process just carries on.”
With frequent rain, this foetid mix would get washed through the sewers to water treatment works, where organic waste is broken down into gases, Evans said.
But in a drought, the fermenting sewage stays in the drains. Evans said: “The microbiological decomposition is currently happening more in the pipes, rather than at the treatment works. And that’s what we’re smelling.”
As a result – and like our digestion – the sewage system “farts and burps”, Evans says. “When microbes get excited they give off a load of gas, so it comes in wafts. It’s a cocktail of methane, [and] a little bit of hydrogen sulphide, which gives the rotten egg smell. There’s also nitrous oxide, which you can’t smell, but it will be in the mix.”
Heat accelerates this microbial activity, according to Simon Clarke, professor of cellular microbiology at the University of Reading. “Bacteria and other microorganisms that decompose organic matter often work more quickly at warmer temperatures, increasing the release of gases that we perceive as unpleasant smells.”
The current stench from the drains is the flip side of creaking system that allows raw sewage to pollute seas and rivers during heavy rain. Evans said: “If you couple the stench with the anxiety about sewage spills, it all points to wastewater system that is very old in a world that has changed a lot.”
Unlike sewage spills, the smell, however unpleasant, is not a risk to the public – or at least not yet. Evans said: “If you get a buildup of gas in the sewers, that could be risky, because methane is an inflammable gas. The risk is tiny, so it’s not yet a public health issue; it is more a public wellbeing and pleasantness issue. The reason we’re noticing it is the because we’re at the extreme of what the system can cope with.”
Evans, whose areas of expertise include “faecal sludge management”, said the public and policymakers were squeamish about confronting these issues.
