If storm overflows are designed to deal with rainwater overwhelming the sewage system, why are they sometimes discharging when there has been little or no rain? In 2025, England recorded 291,492 monitored storm-overflow spill events. At first glance, that number is shocking. It works out at almost 800 recorded spill events every day of the year. Yet 2025 was an unusually dry year. In fact, the Environment Agency says the fall in sewage-spill numbers compared with 2024 was heavily influenced by those unusually dry conditions. Spill events fell by 35%, while the total duration of spills fell by 48%. So here's the obvious question: If dry weather reduces sewage spills, why are sewage overflows operating at all when it isn't raining? The answer is complicated — and potentially far more concerning than the headline numbers suggest. What is a storm overflow actually for? To understand the problem, we need to look underground. Many parts of England still have combined sewer systems. ...
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