Take the case of London. Its 21,000-kilometer sewer network was a marvel of the Victorian age when it was constructed. The system ensured that water-borne diseases like cholera disappeared. It also relieved the city of unpleasant smells and significantly improved the overall living conditions.Some 150 years later, the situation has dramatically changed because of increasing population and lack of investment by successive governments to improve London’s sewage system. Today, when there are 2 millimeters or more of rain in an hour, untreated raw sewage flows into the River Thames. This happens on average once a week. Each year, some 30 million tonnes of raw sewage are discharged into the River Thames.