London’s Summer Heat Unleashes Sewer Stench

During an extended spell of temperatures above 30 °C and scant rainfall, residents across London have reported a pervasive, foul smell emanating from storm-water drains. Simon Birkett, founder and director of Clean Air in London, noted that the odor has persisted for weeks and is especially noticeable near open drains. Experts say the drought has halted the usual flushing of raw sewage to treatment works, allowing microbial activity to intensify within the pipe network and release malodorous gases.

The Guardian

London’s underground drainage still relies on the Victorian-era layout devised by civil engineer Joseph Bazalgette in response to the 1858 “Great Stink.” Prof Barbara Evans, chair of public-health engineering at Leeds University, compares the aging network to a “giant intestine,” where the gut-like microbiome continues to decompose organic material. In normal wet conditions, this decomposition occurs at treatment facilities; during the current dry spell, it remains in the sewers, producing the observed stench.

The Guardian

Prof Evans stresses that, while the smell is unpleasant, it does not yet constitute a public-health emergency. She warns that methane buildup in the pipes could become hazardous, though the risk remains small. She argues that the extreme conditions highlight the system’s inability to cope with both hotter, drier periods and intense rain events. Evans recommends separating “grey water” (from sinks and baths) from “black water” (from toilets), a practice already adopted in Sweden and Germany, to maintain hydraulic function even without rainfall. Professor Simon Clarke of the University of Reading adds that bacterial activity also creates the pleasant “petrichor” scent after rain, underscoring the dual role of microbes in urban air quality.

The Guardian

• “There’s been a bad smell around for weeks,” — Simon Birkett, the founder and director of Clean Air in London

The Guardian

• “The microbiological decomposition is currently happening more in the pipes, rather than at the treatment works. And that’s what we’re smelling.” — Prof Barbara Evans, whose areas of expertise include “faecal sludge management.”

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• “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.” — Prof Barbara Evans, whose areas of expertise include “faecal sludge management.”

The Guardian

• “Bacteria are also responsible for one of the finest and most iconic smells of a British summer: the petrichor smell of summer rain, which occurs when bacteria in the soil are released by the rain and reach our noses. You don’t need to be a microbiologist to appreciate the beauty of that.” — Clarke. He

The Guardian