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Information, guidance & standards

Storm overflows

100,000 kilometres of England’s sewer pipes were built before the mid-1960s and use an old-fashioned design that carries two kinds of waste: rainwater from street drains, and sewage from homes.

They are therefore known as ‘combined’ sewers. Combined sewers were built many decades before modern rates of population growth and climate change were understood, which means that there is often now more sewage and rainwater going into these systems than first envisaged.